RPM Goes Mainstream

It's certainly true that I haven't posted an article here on 196,800 Revolutions Per Minute since May. Despite this, I am having more success blogging about small arms technology than I ever thought I would.

The few readers I have will already know that I am now full-time blogging at TheFirearmBlog.com. Instead of posting an article every month here, and accepting a modest check from Google, I am blogging full time at TFB, posting thirteen articles per week and covering both big and small topics. I have essentially complete creative control there; there is a considerable degree of separation between the people who pay the bills and those who do the writing. I won't pull the curtain back too much on TFB, but the content you see from me there is what you would get were I posting on my own time here (except I can post much, much more often at TFB, thanks to not having to work as much). When I first started working there, I was concerned that I would be forced to post on topics I did not care about, or that there would be a lot of micro-managing coming from the top. Not only did this not turn out to be the case, but thanks to the paycheck I get there I can buy more books (and I have more time to read them), meaning I am essentially working full time to bring my readers the best writing that I can, informed by both the additional resources at my disposal and by the extra opportunities being a writer there affords me. Indeed, so complete has my control over my content been as a writer for TFB that this blog has remained without update for so long; originally, I planned to continue posting here those articles I felt didn't fit in TFB, or would be too risque to ask the bosses to pay for. So far, it has been the case that no articles I have written proved unsuitable for TFB, and this blog has been all but abandoned as a result.

Steve asked me once if I enjoyed writing for TFB - he maintains that he wants his writers to enjoy their work. In truth, writing for them has been nothing short of magical for me. I am employed doing what I love (running my mouth - err, fingers), as a result of this I can write articles I never would have been able to without being paid, and I reach an audience that few other history-oriented bloggers do.

RPM will be updated again - if and when I find something appropriate that does not pass muster at TFB. In the meantime, I'd like to share a few articles I've written that I feel are among my best, as well as my contact information.

Before The Sturmgewehr: Assault Rifle Developments Prior to 1942
Energy: Don’t Sweat It!
A Short (Stroke) History of Tappet Operation, Part I: How It Works
Firearms Semantics: “Battle Rifle” and “Assault Rifle”
A Short (Stroke) History of Tappet Operation, Part II: Early Tappet Designs
How To Find Case Capacity With SolidWorks
A Short (Stroke) History of Tappet Operation, Part III: The M1 Carbine Cometh
The US Army Marksmanship Unit’s .264 USA
8 Uncommon Rifle Shooting Tips For Beginners
Ten 20th Century Military Rifles History Has Forgotten
Hindsight Is 30/06: A Critique Of The M1 Garand
Small Arms Technology: Has It Really Plateaued?

Contact info:
Email: nathaniel.f@staff.thefirearmblog.com
Twitter: @TFB_Nathaniel_F

Are U.S. Soldiers Dying From Inadequate Weapons? No.

I dislike doing rebuttal posts. The temptation is strong to adopt a simple quote-and-refute style, which costs little time and allows me to return to my only modestly interesting but very necessary daily life. This style is only compatible with lazy writing, however, and it's bad form to use it too often. Even so, there is a need for a direct response to some works of "journalism" which rely on sensationalist headlines over content to get attention, and which spread falsehoods, misconceptions, and sometimes even outright lies in the process.

I was asked by a friend what I thought about this hit piece on the M16/M4 platform and the 5.56mm caliber, which I decided offered me an opportunity to write a little more about the subject. As if anyone felt I hadn't already written enough, that is. Interestingly, the piece was written by Tom Kratman - a name I had to google - who is apparently a veteran of the 5th Special Forces Group and of 19 years in regular Army, eventually retiring at O-5 (the same as my father, of a different branch, coincidentally). He also writes science fiction for Baen, the same publisher where the old THR (a major haunt of mine, once upon a time) moderator Larry Correia now writes.

Kratman is then no neophyte as a writer or novice to military thinking, but this in my opinion only lends a hue of bafflement to his two EveryJoe articles. This man was special forces, and an officer, I must keep reminding myself as I read every tired myth, regurgitated piece of gunwriter hype, and mis-remembered factoid.

It is difficult for me to not be critical of the pieces, both from a factual and a writing standpoint. When my inner monologue reads the figures on my liquid crystal display, I am taken back to caffeine-and-pizza fueled spring mornings and afternoons, sitting in one piece chair-desks intended for the tiny Japanese furniture maker who designed them while listening to a youth who hasn't yet learned to shave the few wisps of a Van Dyke growing on his otherwise newborn face wring out a thin argument he decided on a week before. "Write something we can sell," I wonder if that phrase was ever uttered aloud or transmitted via electrons down copper wires during the planning phase of these two articles. Or perhaps Mr. Kratman truly believes in his premature ideas, which are so poorly supported they are in free-fall, about to reach terminal velocity.

"Remember, he was in 5th Special Forces Group, and a Lieutenant Colonel," again.

Let's step back. Many people disagree with me regarding my opinions of the AR-15 rifle family and the 5.56mm cartridge especially. Some of those people, I can hold a discourse with, and present the evidence I have for my position as best I can, to reach a mutual understanding of ideas, experiences, and views which led our opinions to where they are. Some I cannot, because they are too used to fighting the good fight; too zealous for a true mutual discourse.

Many more are too wrapped up in thin premises fed to them via casual reading of the latest issues of tactical magazines in the Barnes & Noble to really have a decent conversation with. It's this last kind that Mr. Kratman most closely resembles, from his escape-velocity exaggeration of the differences in capability of the M4 carbine and M16 rifle, to his mis-placed snark about the vagueness of the ACR program from the 1980s and 1990s. This last plays off an assumption that isn't true - that the ACR program demanded a deliberately vague "100% improvement" over the M16, begetting the almost laughably inane comment: "That means that we will never have a rifle that’s 99% better." In truth, the ACR program's goal was very specific: The winning rifle had to demonstrate a 100% improvement in hit probability during a highly sophisticated course designed specifically to measure that factor with soldiers under combat stress.

None of the rifles even came close. None of the advanced concepts, not burst fire, not caseless ammunition, not four power optical sights, improved the probability of a hit anywhere close to 100% over the M16A2 rifle. Those design elements that did significantly aid the hit probability - most notably optical sights - were incorporated into future AR-15 pattern service rifles and are in use today. To Mr. Kratman, however, the M4A1 with laser, CCO, vertical grip, and light might as well be an M16A2. The degree to which this is true is irrelevant - A G11 might as well be an M16A2 in terms of hit probability, something that Mr. Kratman ignores in favor of the white-noise-esque "they're failing our boys!" drone.

Kratman rounds out the article with more sophomoric whinging dressed as snark, and an off comment about the French. "A Lieutenant Colonel and veteran of the 5th SFG..." Yes, of course, I mustn't forget.

His follow up begins by repeating another half-truth about the M16; that the Army never wanted it and it was all McNamara's fault, a "fact" that ignores that the Army agreed to cancel M14 production in favor of the extremely ambitious SPIW, and McNamara was forcing them to, you know, actually provide rifles to the troops in the meantime. It may be presumptuous of me to think that this is something armies are expected to do, but I'll risk it. Eventually, SPIW crashed and burned, and the surprisingly good M16 became the mainstay of the Army for a half-century. None of this matters to Kratman, of course, since it doesn't make for good copy.

Where some sensationalist gunwriters would take a "back to basics" tack, and suggest re-adopting the M14 in .280 British or some such nonsense, Kratman instead talks about some potential technological improvements that could be in the pipeline for small arms, along with a number of other things that rifle salesmen want you to believe are technological improvements, but actually aren't. His list goes: 1. Intermediate-intermediate calibers, 2. Hyper burst, 3. Carbon-fiber barrels, 4. Electronic ignition, 5. Plastic cased ammunition, 6. Caseless ammunition, 7. A gas piston operating rod, and 8. Optical sights. 2, 3, 4, and 5 fit in with potential technologies that could improve the rifles of the future, 1 and 7 mostly sell rifles, not really offering anything over the 5.56mm cartridge and the AR-15 platform, 6 is all but dead due to technical issues, and 8 has already been implemented, further calcifying my suspicion that Mr. Kratman's technical knowledge of the subject is stuck in 1991.

What's strange is that he doesn't use this list to paint a rosy picture of the future of small arms in contrast to its oft-claimed stagnation; he uses it (in yet another attempt) to bash the M16. As if, somehow, they could have issued rifles then in 1964 that utilized technologies that are just now maturing to a basic level of feasibility. Some early AR series rifles did trial composite barrels and carbon-fiber handguards, features subsequently deleted in later versions because they didn't work very well then. It's as if Mr. Kratman doesn't understand that just having a working prototype doesn't mean you can make ten million rugged, mature, combat-ready weapons.

"A Lieutenant Colonel and veteran of the 5th SFG," I must remind myself.

It's bizarre to read a piece so sophomoric and poorly researched and constructed, only to follow the authorship trail and read a biography that impressive. Simply put, while I do not demand that everything I read reinforce my own opinions and ideas, I do not expect this sort of thing from a Special Forces Group veteran, much less one who's an O-5 rank and who gets paid to write for a living.

On Combat Shooting (Part II)

Anthony G. Williams, in his article Assault Rifles And Their Ammunition: History and Prospects cites this line from Dual Path Strategy Series: Part III - Soldier Battlefield Effectiveness written by the PEO Soldier G5, Strategic Communications Office in August of 2011, to support his idea for a 6.5mm general purpose cartridge (GPC):

"Ultimately, Army service rifles must be general purpose in nature and embody a series of tradeoffs that balance optimum performance for a wide range of possible missions in a range of operating environments. With global missions taking Soldiers from islands to mountains and jungles to deserts, the Army can’t buy 1.1 million new service rifles every time it’s called upon to operate in a different environment."

However, earlier in that paper is contained this section on the range of the rifleman:

The maximum effective range of a weapon system is also a key element as it represents the potential for how far out a Soldier can effectively engage the enemy. This is also critical as it affects a Soldier’s ability to leverage an overmatch advantage. Doctrinally, this means that a Soldier will look to engage the enemy at a range that is greater than the range at which they can be engaged by enemy fire (typically 20 percent). According to FM 3-22.9, Rifle Marksmanship M16/M4 Series, there are three ranges of concern. First, there is the detection range, which must be well beyond the effective range of the weapon system. This provides the Soldier time to prepare to engage the enemy at the farthest possible ranges. The next band is the range overmatch distance, whereby friendly Soldiers can engage the enemy, but the enemy cannot engage the Soldiers. The final band is the threat engagement range where enemy personnel can target friendly forces.

Optimally, friendly forces will engage as the enemy enters the range overmatch area. This advantage is short lived however, since a quickly approaching enemy can move through this area in seconds. For example, according to The Encyclopedia of Land Warfare in the 20th Century, the effective range for AK-47 fired on semi automatic is 400 meters. The effective range for an M4 Carbine is 500 meters. The 100 meter difference provides a decisive range overmatch capability so long as Soldiers are proficient at hitting targets at the 400-500 meter range, which is why extensive marksmanship training is so critical.

The range of a weapon system relies heavily on the ammunition the weapon fires and the length of the barrel. Systems that utilize 5.56mm ammunition typically cite ranges of 500 – 550 meters for point targets while U.S. weapon systems that fire 7.62x51mm typically cite ranges closer to 800 meters for point targets. The rounds actually travel further but tend to destabilize after they slow to subsonic speeds and therefore lose accuracy. Longer barrels allow more of the propellant's energy to be transferred to the projectile, resulting in greater range. The spiral grooves inside a rifled barrel impart spin to the round. The spin stabilizes the round which provides accuracy, though it doesn’t necessarily increase the average range of the system.

Regardless of the range potential for certain weapon platforms, the human factor must be considered. Studies have shown that Soldiers can only consistently hit a human-size target more than 300 meters away 50 percent of the time or less on a qualification range. The numbers are significantly lower when a Soldier is operating in high stress environments. 

Therefore, whether a Soldier is firing a 5.56mm system with an effective range of 500 meters, or a 7.62mm platform with an effective range of 800 meters, what really matters is whether he or she has the skill to hit the target to begin with. Taking the human factor into account, one could argue that the “real world” effective range of a 5.56 system is similar to a 7.62mm weapon platform because the range potential of both platforms significantly exceeds the average Soldier’s marksmanship ability. This is not to say that exceptional Soldiers such as U.S. Army Snipers and Squad Designated Marksmen with specialized training are not fully capable of firing small arms to their maximum potential.

The value of having a system capable of increased range not only depends upon the skill of the operator, but it also depends upon the operating environment. In urban or restrictive terrain, for example, most line-of-sight ranges are significantly less than a weapon’s range potential. In more open terrain, the engagement range increase. For example, according to Lt. Col. Henthorn, in operating environments like Iraq, 80 percent of engagements are less than 200 meters. While in more distributed environments like Afghanistan, only 50 percent of engagements are less than 300 meters. 

What this is essentially saying is that the well-trained rifleman is effective out to 500 meters regardless of the caliber of rifle he is using, even though, in Afghanistan, approximately half of engagements occur beyond 300 meters. Given this, how would issuing GPC-caliber infantry rifles help the rifleman to be more effective?

The paper goes on to talk more about the general purpose round as they define it. Contrary to what Wr. Williams's citation implies, the author of the paper considers the M855A1 EPR to be a true general purpose cartridge, as it can engage a wide variety of targets reliably within the effective range of the rifle. This indicates that what Mr. Williams and the author of the paper (and, indeed, the US Army) mean by "general purpose" ammunition is different.

Regardless, I recommend that the reader follow the link and read the whole thing.

Momentum Has Nothing to Do With Stopping Power

There is a major misconception that pops up often in discussions of small arms: That momentum reflects in some way the terminal effect that a projectile has on a human target. It seems to be standard in the gun journalism industry when evaluating new calibers for game or war to test them against steel poppers, implying or even outright stating that this informs the terminal effect of the round. Even Larry Vickers, to whom I am not even close in terms of experience, says in this video about PDWs that the low momentum produced by the 4.6x30 round - making it unable to knock down the steel target - is a "clue" to low terminal performance.

Now, I have little expectation that a 4.6x30 round, which produces about 540J from the MP7, will perform much better against a human target or gel block than a 9mm JHP or even FMJ. It may more consistently perform after penetrating ribs, but in general, the round is limited in its effectiveness by its low muzzle energy, and its ability to deposit that energy in the target (link starts a download). However, is what Larry says true? Is low momentum a "clue" that a round might not have very good terminal effectiveness? Well, I don't really think so. Sure, a cartridge with marginal terminal effectiveness, like the 4.6x30, might have low linear momentum. However, a cartridge like .45 ACP, which in hardball form produces no greater energy than the 4.6x30, produces more than two and a half times the linear momentum; comparable to the much, much more effective 5.56mm round, in fact.

Because of all the variables involved in the problem of terminal effectiveness against human targets - including the target's mental state, the perceptions of the shooter, and most important, the location of the hit - it can be difficult to say what is and is not relevant to the total sum of terminal effect. However, momentum is one metric that can be discounted entirely. Consider that when a gun fires, it creates a force going in two directions, the bullet and gas going forward, and the firearm itself going backward. This force acts on both bodies over the same length of time - that is, however long (and a little after, due to muzzle thrust) the bullet is in the barrel. Because the forces pushing the bullet and gas out the barrel, and pushing the gun backwards against the shooter's shoulder are equal and act over the same length of time, the momentum of the sum of the bullet and the gas propelling it, and the rifle recoiling, is the same. This means that the momentum of the rifle recoiling into your shoulder as you fire will always be greater than the momentum of the bullet as it hits the target, for two reasons. First, because the gases escaping from the muzzle account for momentum lost, and because the bullet loses velocity - and thus momentum - as it flies downrange, whereas the rifle doesn't have to travel to recoil into your shoulder.

However, we observe as the unspoken first law of shooting that guns have a deadly end, and a non-deadly end. If momentum informed the terminal effect of a weapon against living targets, we'd all be dead fools.

So remember, the next time you're shooting silhouette targets with your .45 ACP 1911 and they fall with a satisfying "clunk" to the ground, the only game the momentum of that 230gr hardball ever felled were made of AR500 steel.

Check me out at The Firearm Blog!

About a month and a half ago, I was contacted by Steve of The Firearm Blog to re-post my article The Case Against A General Purpose Cartridge up at his website. After a short conversation, he decided to hire me on as a monthly writer. So far, I've written two articles for them, so my readers should go check them out!

The General Purpose Cartridge Revisited

I've come under some fire on Internet forums for "misrepresenting" the GPC concept as being heavier than it would in actuality. While I feel that the concept in my The Case Against article - though constrained by several requirements set forth by some members on Mr. Williams' forum - is a perfectly valid approximation, today I hope to address this complaint by creating the absolute lightest GPC estimate I possibly can while still sticking to conventional ammunition design and fulfilling the basic requirement that it not have any less residual energy at 1,000 m than M80 Ball.

First, I need to recall that M80 produces just over 410 J at that range (.195 G7 BC, 2,750 ft/s muzzle velocity, Army Metro atmospheric conditions). You can see this for yourself if you head over to JBM's ballistic calculator and plug in the appropriate values. My GPC must meet or exceed this value. To really get the lightest weight possible, I'm going to need a very good form factor for my bullet- since this is all about retained energy at range. The best form factor I know of for a service projectile is .889 i7, and belongs (paradoxically) to the first spitzer rifle bullet to see service, the French Balle D, an all-brass 12.8 gram boattail projectile with a fairly unique design. If I scale that bullet down to .264" caliber, it weighs just under 7.2 grams.

Since the Army has spent a bunch of time, money, and effort refining their M855A1 EPR design, it seems unlikely that any new caliber would have a substantially different projectile design. Fortunately, I only need to make moderate changes to the Balle D to accommodate this. The scaled-down projectile will be slightly longer - proportionally - than the original at 33.5mm in length, as well as slightly lighter at 7.0 grams. Now, I can find my ballistic coefficient, which works out to a very impressive .249 G7. Running that through JBM a few times tells me I need a muzzle velocity of 2,800 ft/s to meet M80's energy  at a kilometer:

These are some very impressive ballistics! Now, let's see how much this performer would weigh. To shave as much weight as possible from the design, I am going to use M855A1's peak pressure of 62,000 PSI, as well as the same case taper and shoulder angle of 5.56. Many have argued that 62,000 PSI is too much pressure for a rifle cartridge, and that 5.56's case taper and shoulder angle are a detriment to its reliability in automatic weapons, which is part of the reason why my last estimate was so heavy. This time around, I'm pulling out all the stops; no expense will be spared making this GPC as light as I can. In my opinion, the .5 degrees case taper and 23 degree shoulder of the 5.56mm are adequate, and the 62,000 PSI peak pressure is made safe by more thermally stable propellants. I will move on.

After doing several run throughs with the Powley computer, I found that about 41 grains case capacity was needed to generate the sort of performance I was looking for from 20" barrels (this, as far as I know, being the length of barrel chosen by Mr. Williams as optimum for his GPC). Using Solidworks, I created a fairly svelte case: based on the .30 Remington case head and only 46.4mm long, it has almost exactly 41 grains case capacity:

Here are the Powley results for my completed cartridge:

Judging by the propellant weights of both the 6.8 SPC and the 6.5 Grendel, though, that 29.1 grain charge weight seems a little light to me. A spit-in-the-wind estimate puts me at 34.7 grains charge, which sounds more reasonable. Now, we can figure out how much the cartridge weighs.

The bullet, of course, will be 7.00 grams. Large rifle primers weigh about .35 grams, as I mentioned in The Case Against. The charge, in metric, works out to 2.25 grams, and the case itself weighs 7.39 grams if made of brass, or 6.91 grams if made of steel. I will assume steel-cased ammunition, which gives me a total weight of 16.51 grams per cartridge (16.99 grams for brass). 16.5 grams is absolutely fantastic, and lighter even than Mr. Williams' target weight for a GPC with a 7 gram bullet. Let's look at what that means for the infantry platoon:

Weight of ammunition (only, not including magazines or links) of infantry squad breakdown by squad role: 

Squad Leader: 210 rounds 5.56mm, totaling 2.54 kg
Team Leader: 210 rounds 5.56mm in magazines, 200 rounds linked 5.56mm for M249 totalling 4.96 kg (x2)
Automatic Rifleman: 800 rounds linked 5.56mm, totaling 9.68 kg (x2)
Grenadier: 210 rounds 5.56mm in magazines, 200 rounds linked 5.56mm for M249 totaling 4.96 kg (x2)
Rifleman: 210 rounds 5.56mm in magazines, 200 rounds linked 5.56mm for M249 totaling 4.96 kg (x2) 

Weight of ammunition of infantry squad: 51.7 kg (x3) 

Weight of ammunition of infantry squad with 16.5 gram GPC: 70.5 (x3) 

Weight of ammunition of infantry squad with 20 gram GPC: 85.4 kg (x3) 

Weight of ammunition of infantry squad with M240s in place of M249s: 85.5 kg (x3)

Weight of ammunition (only, not including magazines or links) of weapons squad breakdown by squad role: 

Squad Leader: 210 rounds 5.56mm, totaling 2.54kg
Machine Gunner: 300 rounds linked 7.62mm, totaling 7.26 kg (x2)
Assistant Gunners: 210 rounds 5.56mm in magazines, 400 rounds linked 7.62mm for M240 totaling 12.22 kg (x2)
Ammunition Bearer: 210 rounds 5.56mm in magazines, 300 rounds linked 7.62mm for M240, 140 rounds 7.62mm in magazines totaling 13.2 kg (x2) 

Weight of ammunition of weapons squad: 64.5 kg  

Weight of ammunition of weapons squad with 16.5 gram GPC: 53.0 kg

Weight of ammunition of weapons squad with 20 gram GPC: 63.8 kg

Weight of ammunition (only, not including magazines or links) of platoon headquarters breakdown by squad role 

Platoon Leader: 210 rounds 5.56mm, totaling 2.54 kg
Platoon Sergeant: 210 rounds 5.56mm, totaling 2.54 kg
Radio Operator: 210 rounds 5.56mm, totaling 2.54 kg
Combat Medic: 210 rounds 5.56mm, totaling 2.54 kg 

Weight of ammunition of platoon headquarters: 10.2 kg  

Weight of ammunition of platoon headquarters with 16.5 gram GPC: 13.4 kg

Weight of ammunition of platoon headquarters with 20 gram GPC: 16.8 kg 

  

Total weight of ammunition in the platoon: 229.3 kg    

Total weight of ammunition in the platoon with 16.5 gram GPC: 277.9 kg

Total weight of ammunition in the platoon with 20 gram GPC: 336.8 kg 

Total weight of ammunition in the platoon with M240s in place of M249s: 330.9 kg 

Weight increase in the platoon if Carl Gustafs are issued in place of 60mm mortars: 47.5 kg

As my readers can see, even this extremely optimistic estimate still adds almost fifty kilograms of ammunition to the infantry platoon (to say nothing of the increase in weight from the heavier belt links, magazines, and weapons that would be needed to chamber the cartridge). I've heard some GPC proponents claim that the savings in weight of a GPC vs. 7.62mm would balance out its increased weight vs. 5.56mm weapons at the platoon level; this is clearly not true. The GPC - even the lightest possible GPC - represents a significant weight increase for the infantry rifle platoon (or a corresponding reduction in rounds carried). Further, even replacing the platoon's 60mm mortars with direct-fire recoilless rifles is lighter than switching whole hog to the GPC. The Army has already decided to introduce Carl Gustafs to the infantry, which in my mind neatly solves the issue of having to call in air or artillery support when under fire from long-range Taliban ambushes; this being the primary rationale for the GPC in the first place. If the mortars are left home, American soldiers will be able to project high explosive firepower at long ranges without the need for an expensive and time consuming ammunition change-over, and with no more additional burden at the platoon level than would result from fielding a GPC.

This cartridge I've designed is an impressive ballistic hot rod. It would make some sense for 7.62mm weapons to be replaced with weapons in a similar caliber, retaining the capability of that round while slashing the weight of ammunition by about 30%. I felt much the same in my initial article about my 20 gram GPC estimate. Anything that reduces the soldier's load without reducing capability or introducing problems is probably worth doing, if you can afford it. What I disagree with is the idea that a cartridge such as this should be a general purpose cartridge; that it should be issued to riflemen as well as designated marksmen, machine gunners, and as ammunition for static machine guns. The additional weight of ammunition and rifles, and increased recoil and size, sours the idea considerably in my mind vs. the two caliber system.

Called It!

I don't normally reblog without commentary, but it seems my earlier notion that the Carl Gustav could be issued in the general Army as a way to improve infantry effectiveness at long range has proven prescient.

.300 AAC Blackout: The End of 5.56?

This PDF from Advanced Armament Corp extolling the virtues of the .300 AAC Blackout vs. 5.56mm includes a curious section:

Boy those sure are some impressive numbers for an overgrown .30 Carbine! Do they reflect reality, though? Let's check JBM's ballistic calculator. First, we'll need to find a ballistic coefficient figure that reflects a 125gr .300 Blackout load. Here's a very impressive looking Sierra 125gr Matchking, but it's BC is in G1, not G7 like we want. Fortunately for us, JBM has a drag function converter. Using this, we get a G7 ballistic coefficient at 2,220 ft/s of .170. Now we can plug all this into JBM's trajectory calculator to see if AAC's claims are accurate. For this, we'll leave energy in ft-lbs, but change range to be in meters:

That's... Pretty much right on the money for AAC's claims. What about their numbers for 5.56mm?

Not even close, for trajectory.

Reevaluating this, if we take 5.56's performance at 500m as a baseline for "maximum effective range", then it out-ranges .300 AAC Blackout by about 110m. Further, it's worth noting that at 250m, 5.56 has less than a quarter of the drop, thanks to its laser-like trajectory, which enables the 25 yard combat zero. Worse, 5.56 actually generates slightly more energy per pound than the 125gr .300 AAC Blackout, with 23.8 ft-lbs/gram, vs. 22.7 ft-lbs/gram (how about those units? Working in firearms sure is fun!). It's also worth remembering that larger FMJs tumble less readily than smaller ones and will deposit less of their energy into a human target, something I can't seem to repeat often enough.

So does all this make the .300 AAC Blackout a bad cartridge? No, I don't think so. It seems like an interesting concept, being able to switch from a quiet subsonic cartridge to a harder-hitting and longer-ranged supersonic one without changing any hardware other than the magazine. Of course, the high speed low drag types in my audience will have to tell me whether that sort of concept is attractive to anyone other than readers of Tactical Life magazine, but it's certainly still worth looking at.

What this does remind us is to trust but verify any data you see in a manufacturer's pamphlet or public materials. In this case, it really does seem like AAC had no problem "massaging" the numbers to make their cartridge look better than it really is.

On Long Range Combat Shooting

Several times on Internet fora I have been challenged for a "discrepancy" in my position on small arms ballistics, that my claims of having shot man sized targets with 5.56mm weapons out to 900 yards didn't mesh with my assertion that infantrymen are going to have a very, very difficult time hitting anything beyond 500 meters. I've responded to this in various ways over the years (something I've found difficult, never having given military service myself), but here's Chris Hernandez on the matter (H/T, Weaponsman):

Second thing: For most modern combat, 300 meters is plenty far. I carried an M14EBR (Enhanced Battle Rifle) in Afghanistan, and I could consistently hit a torso-sized rock at 900 meters – at the range, with perfect weather conditions, a good firing position, on a stationary target at a known distance. In combat, with extreme heat or cold, unknown distances, hasty firing positions, adrenaline and moving targets, plus little annoyances like incoming fire, I would have been ecstatic to smoke a mofo at 200 meters.

Every now and again, the stars will align, and a (usually very good) shooter will get a chance to hit targets in combat beyond 500 meters, but this is very rare. Even so, specialized 5.56mm ammunition seems to perform decently at these ranges.

Go forth and read the whole article (which is about optics selection).

Accurate Barrel Life Calculator

Here's a barrel life calculator I picked up while in school. It estimates the useful barrel life of a cartridge, given the input parameters.

A few examples:

M855:

	Accurate Barrel Life
	Bullet dia [in]	0.223
	Loaded Powder [gr]	25.2
	Powder heat potential [KJ/Kg]	3880
	Pressure [Psi]	58000
	Moly Coating [Y/N]	n
	Total	3049

M80:

	Accurate Barrel Life
	Bullet dia [in]	0.308
	Loaded Powder [gr]	46
	Powder heat potential [KJ/Kg]	3990
	Pressure [Psi]	62000
	Moly Coating [Y/N]	n
	Total	2660

6.5/8/800:

	Accurate Barrel Life
	Bullet dia [in]	0.264
	Loaded Powder [gr]	36.3
	Powder heat potential [KJ/Kg]	3890
	Pressure [Psi]	55000
	Moly Coating [Y/N]	n
	Total	2951

It's important to note that this calculator is most useful for precision shooting, but I think in general the results can be multiplied by about 5 to gain an idea of the useful military life of a barrel. Of course, numerous factors influence how toasty a cartridge is to a barrel, including what the barrel's made of, how high the flame temperature of the powder is, and how the bullet is constructed, so this value should only be used to give the user an idea of how much their design will aggravate these factors.

Comparing 85gr TSX 6.8mm to 5.56

At the request of commenter Angus McThag, I will do a (short) comparison of the 6.8 SPC loaded with the 85gr Barnes TSX to simulated M855 and M193 loads. I already whipped up a simulated M855 load in my previous post about 5.56 replacements, and I will be referring to that regularly through this article, instead of duplicating the information here. In addition, I will not be using Solidworks models for this estimate, as a reasonable estimate can be attained without doing so.

In order to make the comparison as even as possible, I need to create a Powley computer performance estimate. While using the Powley computer may not necessarily give the most accurate numbers in terms of performance for a given cartridge, it does provide the most even basis I know of for comparison. In this case, our 85gr 6.8 SPC provides a somewhat sedate 2,770 ft/s with an 85gr bullet:

As you can see, the peak pressure in this example is only 55,000 PSI, vs. the 58,000 PSI used in my last comparison. It is lower because 55,000 PSI is the maximum average pressure of 6.8 SPC according to SAAMI. If 58,000 PSI is used, the cartridge gains about 30 ft/s. The value of 2,770 ft/s sounded a bit low to me, and I thought maybe the Powley computer was giving me an incorrect result. However, when I adjusted the barrel length to 24" and checked it against Hodgdon's reloading data, I found that it was only about 41 ft/s lower than their value. 41 ft/s is definitely enough to make a difference in the performance of a cartridge, but it doesn't imply some kind of error in the computer itself (individual shots can often vary by more than 40 ft/s). For the same of comparison, I will continue to use the 2,770 ft/s value, instead of adjusting it, while noting that real-world values may be slightly higher.

Plugging this into JBM Ballistics' calculator, we get this (G7 BC is from here):

Just over 300 J at 500m? Jeeze, that's not that great. As we found in my last post on the subject, M855 produces over 400 J at that same range. Well, OK, but which cartridge weighs more? Your first clue is the weight of their respective bullets. Having not rendered 6.8 SPC in Solidworks yet, I can't give you an exact figure, but using the weight from the 6.8 Tech Information page I linked earlier of 28 rounds of ammunition, I estimate that the 85gr 6.8 SPC loading would weigh over 15 grams. Given this, it compares pretty unfavorably to M855, producing only 20.5 J/g at 500m, compared to 35.5 for 5.56.

Why is this value so low? The 85gr TSX is a flat-based bullet, with a poor form factor. It's also pretty light for caliber, and has a fairly low sectional density (about the same as 55gr 5.56)). In light of that, maybe we should compare it to M193:

It only provides 4% more energy at 500m. That's... Rather disappointing. We know that M193 has a cartridge weight of 11.5g, giving it approximately 25.9 J/g at 500m, a full 26% better than the 85gr TSX 6.8. The TSX definitely has the edge in bullet design from a terminal effects standpoint, but those ballistic results simply aren't very impressive.

I don't think I'm very happy with this result. On the chance that the 2,770 ft/s figure is just too low, I tried to dig up the absolute best performance figures I could for the 85gr TSX, and see how they compared to my Powley estimate for M855. I didn't find much, but I did find David Fortier's article on LWRC's Six8 UICW and its special ATK-made 90gr Gold Dot ammunition. Close enough, I think. To get some sort of performance baseline, I did a little math and got an estimated value of 2,940 ft/s from a 14.5" barrel for the 85gr TSX (this is essentially estimating if you pulled the bullet on an ATK 90gr Gold Dot, and reloaded the case, powder and all, with an 85gr TSX, and then fired it from a 14.5" barrel. Of course, this assumes that the values in the article are correct, and I suspect they're a bit optimistic.). Now we're talking. At 500m, this is what it does:

It gains almost 60 J at range from the extra 170 ft/s muzzle velocity, but it still doesn't compare very well to either 5.56, producing only 24.3 J/g at 500m. That's not great performance for a "best case scenario" of the lightweight 6.8mms.

This article illustrates most clearly to me the value of high form factor, long ogive bullets. At the muzzle, the 6.8mm with lightweight bullets looks fairly impressive, but the poor form factors of those bullets really let it down after a half-kilometer. Even by 300m, the initial estimate for the TSX has fallen below M855 in terms of absolute energy, not to mention energy per pound. The 6.8mm cartridge leaves even less space than 5.56 for long ogive, slender bullets, and I think this is the key to understanding its fairly lackluster performance with low sectional density bullets.

How to remove and replace your Vz. 58's fire control group

This article was originally posted on another blog of mine in late 2010, but its content is more appropriate here, I think.

I'm going to deviate a little bit from the established nature of this blog, simply because I like to play Good Samaritan every so often and actually add useful content to the Internets.

You see, recently, I purchased a Vz. 58 steel trigger, to replace the plastic trigger my CZ-USA Vz. 58 came with. When I looked on the Internet for info on how to muck around inside the receiver, I found nothing, so I had to figure it out myself. Trying to remove the fire control group from this rifle without knowing how is really hard, and results in lots of unnecessary scrapes on your receiver, and a lot of fruitless banging and frustration. Removing the FCG after you know what to do, however, is really quite easy, if a bit tricky. I decided to write this to help people do it the easy way.

The parts can get a bit confusing. I use the same terminology Czechpoint does, and you can find a nearly complete parts list for the Vz. 58 at their website:
http://www.czechpoint-usa.com/products/spare-parts-and-accessories/vz-58-parts-and-accessories/
The title is not so much an accurate description of the content as it is all the search terms I used in trying to find info about how to perform surgery on my Vz.

Let's begin.

Firstly, and most importantly, you want to remove the magazine and clear the chamber.

Then, and this is why that last step was so important, you want to flick the safety off if it wasn't already, and pull the trigger.

If you followed step one, you should get a click. If you didn't, you should get temporary hearing loss and a hole in something.

Now, push out the receiver cover retaining pin. This pin likes to push out most of the way and leave about a fifth of itself still retaining the cover, so make sure it's all the way out. If you have difficulty removing the cover, this is almost certainly the problem.

Next, remove the receiver cover by pushing it forward from the rear, and lifting it up. It should come straight on out. Note the dual captive springs; it's important to line them up properly during reassembly.

Now, remove the bolt carrier assembly by retracting it all the way to the rear, and removing it from the top.

Finally, you can inspect the glory that is the Vz. 58 fire control group. When I first tried to remove the old trigger, I just banged on the trigger axis pin until I destroyed two pulled 7.62x54R bullets and gave up that approach. It turns out, the Czechs thought of their trigger axis and sear axis pins backing out and put in two little e-clips.

These e-clips hold the pins in despite the application of considerable hammering. These e-clips are simple to remove, but for God's sake do not lose them. Just take a screwdriver, or other fine implement, and flick them out. They come off readily.

Once both e-clips for the sear and trigger pins are off, tap the two pins out slightly from the left to the right. Tap the sear pin out first, then the trigger pin. Once they come out about a millimeter, there's enough space for you pull them out all the way with a screwdriver or your fingernails. They shouldn't fit tightly.

It'll take a little finagling, but it should be pretty easy to remove the sear.

Once you have, remove the trigger assembly. To do this, press the trigger up from the bottom, and compress the disconnector spring enough that the trigger and disconnector come free from the sear assembly.

Now you have the trigger assembly in your hands. To install your brand new trigger, simply tap out the disconnector pin holding the trigger and disconnector together, and remove the disconnector and disconnector spring.

Replace trigger, or work on the trigger, or make sweet love to it, or whatever you're going to do, and then prepare to go insane.

This next step is the only truly hard part in replacing the trigger on a Vz. 58. You must reassemble the trigger group, which means reinserting the disconnector spring, and then compressing the disconnector to just the right place that the holes line up, while holding the trigger assembly steady, and hammering the disconnector pin back into the assembly. You might be able to more easily do that with a pin vise, but I don't have one of those, so I enlisted my girlfriend to supply the requisite third hand, but found that the assembly is actually too small for three hands to fit on the blasted thing without me hammering our thumbs into pulp.

Instead, I found a pair of pliers, and that worked well enough. It's still a matter of trial and error, though, so be patient, and eventually the pin will work its way a little into the disconnector, and then it's just a simple task of tapping the little devil in gently.

Now that you have your trigger assembly back in one piece, you simply have to put it back in the way it came, and then pushing the pin back in. Do not put the e-clip back on the pin until you are 100% sure your trigger group works. I even went so far as to reassemble the entire rifle without the e-clips, just to make sure. Once the trigger is in there satisfactorily, start on the sear assembly.

It looks weird, but it's not difficult to do once you figure out what goes where. The sear assembly likes to come apart, especially that plastic thing, which I'm pretty sure is a replacement for an automatic mechanism, since it does basically nothing. Czechpoint doesn't sell this part, so if it breaks, you're SOL, I guess. Anyway, that do-nothing plastic thing fits with the large end toward the right, if your assembly came apart (mine did), and the sear fits with the long end basically sitting in the middle of the receiver, to hold the striker back before firing.

The sear group fits in so that the little tab jutting out from the bottom of the sear is pulled on by the disconnector. A little trial and error will make it fit properly. Interestingly, the sear and trigger pins are interchangeable, so don't worry that you got them mixed up.

Once your rifle's trigger works, simply slide the e-clips back onto the pins. This is actually easier than it sounds, if you use a screwdriver. They might not click, exactly, but if they look like they're on, they are.

Now you're ready to reassemble the rifle. Simply tilt the muzzle of the rifle downward, let the bolt flop forward in the carrier, and mate the carrier and receiver together at the cutouts in the rifle rails. Slide the bolt forward. Now if the sear engages the striker, that's a good sign. If it doesn't, you have more work to do. Remove the carrier and find out where you screwed up. If it holds the striker, pull the trigger, both to make sure the trigger group will release it properly and to prepare the partially assembled rifle to receive the cover.

Now take the bigger, top spring in the receiver cover, and align it with the topmost hole in the bolt carrier. slide it in, making sure the lower striker spring falls into place inside the striker (they call it a "linear hammer", since the actual firing pin is a separate part). Now slide the cover in most of the way.

Make sure the little tabs jutting down from the inside edge of the cover mate with the receiver, or it won't go on right. Once it's properly inserted, push in the retaining pin, and you're all set.

All 5.56 Replacements Suck

[The title of this blog post was mandated by the 196,800 Revolutions Per Minute Marketing Department]

One of the benefits of having a system that allows me to accurately create cartridges and predict their performance is that I am able to easily make comparisons and evaluate different configurations against each other in terms of weight, size, and performance. I previously used this method to create a standalone cartridge that satisfied Tony Williams' requirements for a GPC in this post. Today, I'm going to use it to create an example cartridge that shows in part why most larger-caliber 5.56 replacements offer virtually nothing over the cartridge they would replace.

First, we whip up a 5.56 load with the Powley computer:

Naturally, I already had the 5.56 case rendered in Solidworks, based off the 5.56 case specification. The figures for projectile length are those of the SS109 projectile, a drawing of which can be found here.

Now, we'll whip up 5.56 necked up to 6.8mm. Let's use 6.8 SPC projectiles, so we'll need the same case length as 6.8 SPC (1.6864")...

We'll need to decide on a neck length for the new cartridge. 6.8 SPC has a relatively long neck, length, so I think we'll just use the neck length of 7.62x39. This'll make a fairly minor difference in performance, and I'm erring on the side of more, not less...

Here's our finished case:

Now, we have to find the case volume. To do this, we need to model the negative of the case interior, like this:

Then, once you have a solid model, we need to find the internal volume:

Alright, now we have the internal volume in grams H2O. Just divide by 1,000 and multiply by 15.43 to get the case capacity in grains H2O, which comes to 30.2 grs.

Now we need to find the length of the bullet we'll be using. Fortunately there's a handy list of these over at JBM Ballistics. The Hornady 110gr V-Max is a 6.8 SPC bullet, and will be fine for this example. It has a length of 1.045. To the Powley computer:

Alright, now we have two sets of performance figures that are about as directly comparable as we're likely to get. Now we need to run them through a ballistic calculator, the best free one of which I am aware being the one at JBM Ballistics. This is, in my experience, a very accurate calculator, that compensates even for nonlinear increases in wave drag at supersonic speeds. So we enter the projectile weight, velocity, caliber, and set the maximum range to 500 meters, range increment to 100 meters, zero to 25 meters, and sight height to 1.5". We also check "ranges in meters", and in a dropdown menu select "Energy (Joules)". Next, we just need to find some accurate ballistic coefficient figures. Fortunately, I have an Excel spreadsheet of such figures on my website, which just so happens to include the value for the .277" Hornady 110gr V-Max. For 5.56, we'll derive a ballistic coefficient value with the same form factor as the V-Max, in the interests of keeping everything fair. We get a value of .159 G7, very close to SS109's .158.

Now we can get a good estimate of the performance of these two cartridges.

5.56:

...and our 6.8/5.56 cartridge with the 110gr V-Max:

Ahah! See? The 6.8mm provides a full 18% more energy at 500m than 5.56! I knew it! Larger calibers really are better!

...Wait, is that the whole picture? After all, isn't the 6.8mm heavier? What good is a military round that produces somewhat more energy per shot if it doesn't end up saving you any weight? Well, to find out exactly how much heavier our 6.8mm is, we need to go back to Solidworks, and find out how heavy the cases of each round are:

We can see from this that the weight of the cases is very comparable. To get the actual weight of each case, we divide the highlighted figure by 1,000, and multiply by 8.4 (approximately the density of drawing brass). For 5.56, we get 6.372 g, and for our 6.8/5.56, we get 6.298 g. Next, we need to find the weight of the powder charge for each. Well, hey, we already know this, it's right there in the Powley computer results. Converting to grams by dividing by 15.43, we get 1.458 g for 5.56, and 1.283 g for our 6.8. Hey! So far the 6.8mm is winning!

There are two more components left. One is the primer. I happen to know that small rifle primers weigh about .25 g, and both are cartridges use SRPs, so we'll add .25 g for both.

The last component is the bullet. We know the bullet weights already; 62gr (4.02g) for 5.56 and 110gr (7.13g) for our 6.8. This is where the 6.8's minor lead in terms of weight gets completely shattered.

Adding it all up, we get a total round weight of 12.1 g for the comparative 5.56 and 15.0 g for our 6.8mm cartridge.

Now, if we take the energy at 500m and divide it by the weight of the cartridge, we can truly begin to compare these two cartridges. For 5.56, we get a value of 35.5 J/g@500m. For our 6.8mm, we get a value of... 33.7 J/g@500m. That's right, in terms of energy retained at range for every gram carried, the much-loathed 5.56mm actually comes out 5% better than its 6.8mm counterpart. Who'd have thought?

Keep in mind that 5.56 also produces a vastly superior trajectory to the 6.8mm cartridge, having a whopping 81% less drop, 19% less wind drift, and 25% better time of flight, at 500m. Further, remember the principles of wounding when looking at these two cartridges. Smaller projectiles, all things being equal, tumble sooner than larger ones. Faster projectiles tend to fragment more dramatically than slower ones. Not only is the 6.8mm projectile much larger, it is also much slower. Therefore, we cannot expect it to exhibit fragmentation except at the absolute closest range, and even then, it will not do so very dramatically. If it tumbles, it will do so later than comparable 5.56 caliber projectiles, and may not deposit very much energy (link begins a download) within a human target.

Is this comparison perfect? No, it makes several compromises in exactness for the sake of clarity. Does it reflect every larger-caliber 5.56 challenger out there? No, but it does give the reader an idea of what effect increasing the caliber and projectile mass and reducing the velocity has on its performance and the overall weight of the cartridge (or, taken in the inverse, one might ask which produces better ballistics, 6.8 SPC or 6.8 SPC necked down to .22 caliber?). It is unfortunate that this material is too technical to be introductory, as it is so fundamental to understanding rifle cartridge design. Much time and effort that has been wasted might not have been if the designers of these medium-caliber intermediate cartridges had understood these principles.

A closing note: This comparison humors the assumptions of many opponents of 5.56 that the amount of energy a cartridge produces per pound carried is the sum worth of that cartridge in combat. I dispelled this notion of "stowed kills" in another post. One should not confuse my demonstrating that 5.56 meets and beats many of these proposals on their own terms with my validating that method of evaluating cartridge performance for infantry rifles.