tag:blogger.com,1999:blog-5557913977913148366.post2885447013033149945..comments2023-07-21T02:26:42.817-07:00Comments on 196,800 Revolutions Per Minute: The General Purpose Cartridge RevisitedNathaniel Fitchhttp://www.blogger.com/profile/15011387972300996469noreply@blogger.comBlogger24125tag:blogger.com,1999:blog-5557913977913148366.post-16315587236121499552015-11-06T19:12:43.581-08:002015-11-06T19:12:43.581-08:00You can hunt deer with a .22 LR in Texas. :)
&quo...You can hunt deer with a .22 LR in Texas. :)<br /><br />"Negligible case taper", you mean more case taper than .30-06? http://196800revolutionsperminute.blogspot.com/2012/11/case-taper-in-military-cartridges.html<br /><br />Weird, because my Colt 6920 works just great with steel cased ammo.<br /><br />The rest of your argument is circular: "We need a 6.Xmm GPC because we do". Sorry, try again, because that's not gonna hold a lot of weight around here.Nathaniel Fitchhttps://www.blogger.com/profile/15011387972300996469noreply@blogger.comtag:blogger.com,1999:blog-5557913977913148366.post-52372956905784363702015-11-06T19:04:17.928-08:002015-11-06T19:04:17.928-08:00No, you don't need enough to kill a horse, jus...No, you don't need enough to kill a horse, just something legal to hunt deer with [being a better stand-in for human targets vis-a-vis size/mass/solidity...]<br /><br />BTW Nat, you have to redo your calcs: you can't use steel for the case material with the .223's negligible case taper: or did you think the Soviet cartridges had so much taper because they liked funny-shaped magazines? It's all about reliability...<br /><br />As for why the GPC is a good idea, you're basing your assumptions upon needing to carry the same # of rounds when the whole point to the GPC is that it does more with less, ie: it will penetrate cover the .223 has to burrow through, and 1 round will be lethal instead of requiring 2 or 3 to do the job. Whatever your feeling, the cold hard fact is that it needs to be 6.35mm or larger [the huge waste of time on 6mm SAW development notwithstanding] since any rifle bore less than .25"dia has problems with capillarity and burst barrels from water occlusion when fighting in wet environments. Tony Williams arguments for 6.5mm are still pertinent, I'm just annoyed that he jumped straight from 6mm [which is too small for the reason above] to 6.5 w/o including the quarter-bore in the argument... ;-)<br /><br />This is why back around Y2K when people were going over the argument on the rec.guns newsgroup over whether the U.S. should keep 5.56mm or revert back to the 7.62NATO [predicated upon feedback from GW 1], I proposed "splitting the difference" with a .25" or 6.5mm bobo [that's a technical term, for youse uninitiated! ;-D] in a case based upon the .25 Remington. Yep, that's right: somebody cribbed the notes and came out with the 6.8SPC abortion with its too large bullet & inadequate BC & SD. Of course, they were hampered by wanting to fit it in the AR-15's magazine: Tony Williams is entirely correct that we need to build the rifle around the cartridge, not keep trying to fit something in a platform that was never ideal & is now quite long in the tooth. And replacing ALL the rifles in the US inventory still isn't going to cost more than one or maybe two of the F35s that will never justify their development costs [using another example of Macnamara-ism run amok!] <br /><br />Let's go back to the drawing board, and come up with a rifle that is truly deserving of issue to our men & women on the bleeding edge. Let's not worry about the Gauss guns in the pipeline; we'll get them eventually, but let's focus on the here & now & utilizing the best practices of established technology [ie, no DI gas system, etc] instead of something pie in the sky in the sweet bye & bye, mmm'kay?Anonymoushttps://www.blogger.com/profile/07610851658311411621noreply@blogger.comtag:blogger.com,1999:blog-5557913977913148366.post-80736524895497731032014-05-13T16:02:52.975-07:002014-05-13T16:02:52.975-07:00I like the .50 as an anti material weapon. It is c...I like the .50 as an anti material weapon. It is common to need to stop an unarmored vehicle used as a IED delivery device. For Armor or Mech infantry the range is very useful, and the weight is of little concern. For light infantry it could be useful if only the HMG wasn't so darned heavy (84 lbs for M-2, more if on a tripod) I would suggest a low rate of fire 120 rpm weapon that used long recoil, weighing perhaps 15 lbs. The very low weight means that the 4 rounds to the pound ammunition could be useful for long range targets discovered by the infantry squad. If the light infantry was supported by a Big Dog robot or a living donkey, more ammunition becomes less of a problem.Don Mhttps://www.blogger.com/profile/06057058763094040058noreply@blogger.comtag:blogger.com,1999:blog-5557913977913148366.post-53153625678078153322014-05-05T13:23:34.662-07:002014-05-05T13:23:34.662-07:005.56mm and SCHV cartridges in general would benefi...5.56mm and SCHV cartridges in general would benefit more from these new technologies than a GPC would, because their projectile weight is a smaller percentage of their overall weight.<br /><br />The bottom line is that a GPC can't do anything that 5.56mm can't do. Why should armies adopt something heavier and no more capable? <br /><br />I am absolutely open to sound arguments on this, but it's about this time the GPC mafia starts yowling about poodleshooters and energy retained at a kilometer, and I can't take that kind of discussion seriously.Nathaniel Fitchhttps://www.blogger.com/profile/15011387972300996469noreply@blogger.comtag:blogger.com,1999:blog-5557913977913148366.post-77702775866535039192014-05-05T11:42:13.713-07:002014-05-05T11:42:13.713-07:00I do believe the 50 has seen its day. However the ...I do believe the 50 has seen its day. However the 50 gatling is a terrifying vehicle(only) weapon. But some armies are using more & more 338 sniper/anti material weapons. Right now the military uses too many calibers. A 338 lapua or Norma could replace the 50 & 30 cal. A more effective GPC would take up the slack. And forget about weight! Newer tech will eventually save considerable weight. New alloys, carbon fiber wrapped barrels, hybrid polymer cased ammo. It's time to think about what can be done & not about what can't.Lujanhttps://www.blogger.com/profile/05626657118750675207noreply@blogger.comtag:blogger.com,1999:blog-5557913977913148366.post-8811353487163438202014-04-04T09:24:53.488-07:002014-04-04T09:24:53.488-07:00Which means that, rather than being forward thinke...Which means that, rather than being forward thinkers, GPC proponants are actually arguing to keep the 19th Century US Army requirement (shared in similar format by ALL of the "full power" service rifle cartridges from the late 19th Century) from the CIVIL WAR that the rifle cartridge be capable of killing or disabling a horse at 1000 yards.<br /><br />Yup, that's what the performance spec of the M80 round calls for -- because the development requirement specifically calls for range and terminal performance no less than the .30-06, which had to meet or exceed the previous US Army performance (.30 Krag), which had to meet or exceed the .45-70 performance, which explicitly called out the anti-equine Pk requirement.<br /><br />And you know what? 7.62x51mm IS a really good round to kill or disable horses at long range with. It's just that it is not a very realistic Pk requirement anymore. . . Geodkythttps://www.blogger.com/profile/09328915597574377444noreply@blogger.comtag:blogger.com,1999:blog-5557913977913148366.post-81571710447275259152014-03-23T14:20:14.653-07:002014-03-23T14:20:14.653-07:00Maybe. However, it's the opinion of some (not ...Maybe. However, it's the opinion of some (not mine) that .50 doesn't do much more than 7.62 on the battlefield, and is mostly kept around as a legacy weapons system. Given that 7.62 can be significantly improved upon, it might then make sense to issue a 7.62-sized cartridge as a replacement for .50 and 7.62 both, if those are your premises. I used .338 Lapua Magnum as an example earlier, but you could also do this with a cartridge no heavier than 7.62, I imagine.Nathaniel Fitchhttps://www.blogger.com/profile/15011387972300996469noreply@blogger.comtag:blogger.com,1999:blog-5557913977913148366.post-82629490009854928492014-03-22T15:30:48.044-07:002014-03-22T15:30:48.044-07:00Bad choice of words there on my part, I didn't...Bad choice of words there on my part, I didn't mean to imply that you actually thought that, just that that was what you'd proposed for this thought exercise.<br /><br />I agree with you in the sense that both the 7.62 and .50 could be replaced by cartridges that are more efficient, but trying to do a GPC on them will only lead to an even worse solution than the GPC is looking like.Someone Elsehttps://www.blogger.com/profile/01879577725836953297noreply@blogger.comtag:blogger.com,1999:blog-5557913977913148366.post-52963630092732131412014-03-22T15:18:12.821-07:002014-03-22T15:18:12.821-07:00If you'd read carefully, you'd have seen t...If you'd read carefully, you'd have seen that I wasn't advocating the idea, but rather saying that if replacement was your goal, it'd make more sense to start with 7.62 and .50 than 5.56mm.Nathaniel Fitchhttps://www.blogger.com/profile/15011387972300996469noreply@blogger.comtag:blogger.com,1999:blog-5557913977913148366.post-7884902995969335212014-03-22T15:14:58.702-07:002014-03-22T15:14:58.702-07:00You want to replace both the 7.62mm and the .50, s...You want to replace both the 7.62mm and the .50, so whatever round you come up with needs to match the .50 in hit probability and penetration, while not weighing much more than the 7.62mm. If you don't keep the weight low, you're just burdening the weapons squad, and if you can't replace the .50, you're burdening them unnecessarily while not reducing the logistics footprint any.<br /><br />How would you achieve this design?Someone Elsehttps://www.blogger.com/profile/01879577725836953297noreply@blogger.comtag:blogger.com,1999:blog-5557913977913148366.post-51921951385599215262014-03-22T12:59:35.017-07:002014-03-22T12:59:35.017-07:00CTA and caseless both have their own problems whic...CTA and caseless both have their own problems which are unlikely to be solved any time soon.<br /><br />However, don't think that those are the only two ways of reducing ammunition weight and bulk.Nathaniel Fitchhttps://www.blogger.com/profile/15011387972300996469noreply@blogger.comtag:blogger.com,1999:blog-5557913977913148366.post-51404944604049003902014-03-22T12:58:07.680-07:002014-03-22T12:58:07.680-07:00Right, thanks.Right, thanks.Someone Elsehttps://www.blogger.com/profile/01879577725836953297noreply@blogger.comtag:blogger.com,1999:blog-5557913977913148366.post-17944580210917598682014-03-22T12:56:47.234-07:002014-03-22T12:56:47.234-07:00To do what you're suggesting, you'd want t...To do what you're suggesting, you'd want to use CTA or caseless, otherwise the ammunition is going to be too big and heavy. Since neither is likely to be adopted any time soon, I'd consider the GPC to be more likely than a .50 and 7.62mm replacement.Someone Elsehttps://www.blogger.com/profile/01879577725836953297noreply@blogger.comtag:blogger.com,1999:blog-5557913977913148366.post-1785957123404830092014-03-22T03:11:11.464-07:002014-03-22T03:11:11.464-07:00BTW, .35 g is the approximate weight of a Large Ri...BTW, .35 g is the approximate weight of a Large Rifle Primer. Small Rifle Primers (such as 5.56 or .221 Fireball use) are approximately .25 g.Nathaniel Fitchhttps://www.blogger.com/profile/15011387972300996469noreply@blogger.comtag:blogger.com,1999:blog-5557913977913148366.post-80713588644294509052014-03-22T03:07:55.084-07:002014-03-22T03:07:55.084-07:00Yes, but for anyone else, that requires swallowing...Yes, but for anyone else, that requires swallowing a whole series of gun-rag marketing and non-logic that really doesn't stand up to a solid analysis.<br /><br />5.56, especially M855A1, works very well out to 500m. It makes an excellent carbine cartridge, and though you could make something better, until you start getting the same or better perforation performance with drastically lighter ammo, you won't see it replaced.<br /><br />Why not? .338 Lapua is more capable than 7.62x51; you could replace a whole slew of <i>belted</i> weapons with one FOW in one caliber. Screw the GPC replacing ammo that isn't inter-compatible anyway (e.g., 5.56 loose and 5.56 belted), you could replace .50 and 7.62x51 in one go, reducing actual commonality issues (e.g., .50 and 7.62mm ammo inside of an Abrams) while reducing the bulk and volume vs. .50 cal ammo.<br /><br />Or, what we have now might be good enough. 7.62x51 and .50 both have their unique perks, too.Nathaniel Fitchhttps://www.blogger.com/profile/15011387972300996469noreply@blogger.comtag:blogger.com,1999:blog-5557913977913148366.post-82961333305803282562014-03-22T02:49:51.199-07:002014-03-22T02:49:51.199-07:00Heh. It's going to be interesting to see how t...Heh. It's going to be interesting to see how the next generation of flechettes look like.Someone Elsehttps://www.blogger.com/profile/01879577725836953297noreply@blogger.comtag:blogger.com,1999:blog-5557913977913148366.post-59435822797921050212014-03-22T02:11:51.270-07:002014-03-22T02:11:51.270-07:00I think that GPC proponents feel both rounds to be...I think that GPC proponents feel both rounds to be underperforming, hence why the both need to be replaced. Of course, of the two, only replacing the 7.62x51mm will realistically result in a decrease in weight soldier's burdens. If you increased the OAL of the 5.56x45mm to 62.6mm, you could use a long, 65gr lead free projectile with a 0.2 G7 BC and a MV of 940 m/s with only a minimal increase in weight. Performance, while not GPC level, would nonetheless be pretty spectacular. <br /><br />I don't see any 7.62x51mm replacement looking more like the .338 Lapua than the 6.5 GPC, though.Someone Elsehttps://www.blogger.com/profile/01879577725836953297noreply@blogger.comtag:blogger.com,1999:blog-5557913977913148366.post-84171619754937574862014-03-22T00:22:10.436-07:002014-03-22T00:22:10.436-07:00Issue flechettes; technical problems with that con...Issue flechettes; technical problems with that concept be damned.Nathaniel Fitchhttps://www.blogger.com/profile/15011387972300996469noreply@blogger.comtag:blogger.com,1999:blog-5557913977913148366.post-44641408075950238142014-03-22T00:21:04.671-07:002014-03-22T00:21:04.671-07:00I have mentioned before that I'm not sure wher...I have mentioned before that I'm not sure where the emphasis on replacing 5.56mm is coming from, other than that it's fashionable to hate on it at the moment. 7.62x51mm seems to clearly be the underperformer in the mix; if you were intent on replacing any small arms caliber, it would seem to me that it would be the one found most wanting.<br /><br />Then, at that point, can the requirements be relaxed a little bit? Maybe what you end up with looks more like .338 Lapua than a 6.5mm GPC. But then, who knows? A lightweight, but still just as capable round would be welcome, too.Nathaniel Fitchhttps://www.blogger.com/profile/15011387972300996469noreply@blogger.comtag:blogger.com,1999:blog-5557913977913148366.post-61822044835734408432014-03-22T00:11:27.721-07:002014-03-22T00:11:27.721-07:00The bullet's performance at 1,000 metres shoul...<a href="http://www.quarry.nildram.co.uk/The%20Next%20Generation.htm" rel="nofollow">The bullet's performance at 1,000 metres should be comparable with the 7.62 M80 ball, as measured by hit probability (a function of trajectory, flight time and susceptibility to wind drift) and damage potential (bullet energy and penetration).</a>Nathaniel Fitchhttps://www.blogger.com/profile/15011387972300996469noreply@blogger.comtag:blogger.com,1999:blog-5557913977913148366.post-22707456551369296592014-03-21T23:56:41.019-07:002014-03-21T23:56:41.019-07:00According to LoadAmmo, the 7.92mm s.S Patrone (htt...According to LoadAmmo, the 7.92mm s.S Patrone (http://img34.imageshack.us/img34/5269/57745371.jpg) scaled down to 5.56mm (http://www.geoffrey-kolbe.com/cgi-bin/drag_working.cgi?unit_length=mm.&weight_unit=grains&bullet_name=Custom+bullet&re_calculate=yes&diameter=5.69&length=24.645&nose=14.667&meplat=0.854&drive_band=5.69&base_diameter=4.817&angle=6&boat_tail=4.119&secant_radius=12&weight=59&density=8.6) would reach around about 904 m/s from a 20" barrel using .221 Fireball brass and the 62kpsi pressure limit you've set. OAL has been increased to 51.23mm, for your reference.<br /><br />If .221 fireball brass is 5.417 grams (http://www.saubier.com/forum/showthread.php?t=21257), the primer 0.35g, the powder 1.089g and the projectile 3.629g, the whole cartridge would weigh 10.485 grams (10.133 grams with a steel case).<br /><br />Performance won't quite be as good as the M855A1 due to the lower MV and weight, but it should be closer to the M855 than the M193, so I don't think the difference will matter much. It would, however, save about 23 kg (not including weight savings due to lighter magazines and rifles).<br /><br />Just for fun, I did a 4.7mm round as well (http://www.geoffrey-kolbe.com/cgi-bin/drag_working.cgi?diameter=4.9&length=22.9565&nose=14.3472&meplat=0.735&drive_band=4.9&base_diameter=3.42323&angle=&boat_tail=5.4929&secant_radius=&unit_length=mm.&bullet_name=&weight=&weight_unit=grains&density=custom_density&custom_density=8.6&boundary_layer=L%2FT). From a .221 Fireball case, with an OAL of 51mm, a truly ridiculous velocity of 1050 m/s will be achieved with 20 grains of powder. This is sufficient to match and better the penetration of the M855A1 out to 1000 metres, and provides a much flatter trajectory with less windage and a shorter ToF. Surprisingly, the barrel life is only 165 rounds less than the M80 according to the spreadsheet you posted last month.<br /><br />Of course, the interesting thing now being discussed by Stan Crist on Tony's forum is what happens with the GPC concept if we go up against a proper army or insurgents who have a lot of body armour. The GPC may just not be able to cut it on those grounds.<br /><br />Which, of course, begs the question: what do you do when your enemies have armour than protects against your light and heavy platoon level rounds?Someone Elsehttps://www.blogger.com/profile/01879577725836953297noreply@blogger.comtag:blogger.com,1999:blog-5557913977913148366.post-70060223995579905072014-03-21T23:56:15.657-07:002014-03-21T23:56:15.657-07:00So, for a typical infantry squad, we have 23.226 k...So, for a typical infantry squad, we have 23.226 kg worth of unlinked ammo (1470 x 15.8), and 50.372 kg worth of linked ammo (2800 x 15.8g rounds, plus 2800 x 2.19g links http://iaaforum.org/forum3/viewtopic.php?f=8&t=8073). That comes to 73.598 kg, by my count. Without the links, that's 67.466 kg.<br /><br />For comparison, including links, the squad load will have 39.452 kg (1.99g x 2800 links, plus 12.1g x 2800 rounds) of linked ammo, for a total of 57.239 kg.<br /><br />Now we come to the weapons squad. We have 20.698 kg of ammunition in magazines (15.8g x 1310 rounds), and 35.980 kg of linked ammo (15.8g x 2000 rounds, plus 2.19g x 2000 links), for a grand total of 56.678 kg (52.298kg without links).<br /><br />The weapons squad, without the GPC, will have 12.705 kg of 5.56mm ammunition in mags (1050 x 12.1g), 6.776 kg of 7.62mm ammunition in mags (280 x 24.2g) and 56.860kg of linked ammunition (2000 x 24.2g, plus 2000 x 4.23g links), for grand total of 76.341kg (67.881kg without links). I don't know why I get a higher weight than you, but I think I've shown enough working that you can probably figure out where I differed from you.<br /><br />The platoon headquarters will have 13.272kg of ammunition with the GPC as well (15.8 x 840 rounds).<br /><br />Total for the platoon? 290.744 kg (with links)/267.968kg (without links). Still more than 30 kg more than the current load out, but 62.932 kg (without links)/48.576 kg (with links) lighter than the current load out with M240s substituted in.<br /><br />So, for all intents and purposes, there's not much difference between our two rounds (except perhaps in link weight), and a squad as it presently is will have an increased burden if a GPC is adopted (of course, British and, it seems, Australian sections would welcome the decrease in weight).<br /><br />One thing that has now occurred to me, and which might perhaps make the whole post above actually contribute something useful, is that a two caliber system consisting of the 6.5x45mm round (either yours or mine, it hardly matters) and a lighter round might be something worth looking at.Someone Elsehttps://www.blogger.com/profile/01879577725836953297noreply@blogger.comtag:blogger.com,1999:blog-5557913977913148366.post-37368888641053323252014-03-21T23:55:26.104-07:002014-03-21T23:55:26.104-07:00Using JBM's Krupp's Formula function, I co...Using JBM's Krupp's Formula function, I compared the two. By 500 metres, the 6.5mm round outperforms (https://www.dropbox.com/s/nw5dvjdp4uwpwaq/6.5x45mm%20GPC%20%28Krupp%29.png) the 7.62mm round (https://www.dropbox.com/s/9iq1bqq1dpftb67/7.62x51mm%20%28Krupp%29.png), and continues to do so. This is further demonstrated using Tony William's proposed indicator for AP penetration (joules/cross-section area in mm2). <br /><br />The 6.5mm projectile has 56.239 J/mm2 at 100 metres, 39.955 J/mm2 at 300, 27.541 J/mm2 at 500, 14.521 J/mm2 at 800 metres and 10.353 J/mm2 at 1000 metres.<br /><br />In comparison, the 7.62mm has 61.535 J/mm2 at 100 metres, 40.577 J/mm2 at 300, 25.559 J/mm2 at 500 metres, 11.529 J/mm2 at 800 metres and 9.154 J/mm2 at 1000 metres.<br /><br />The 7.62mm holds the perforation advantage at common infantry ranges (<300 metres), but the 6.5mm has the advantage at typical DMR and MG ranges.<br /><br />If we next compare penetration (grams x metres/sec divided by mm² according to Tony Williams), the results are much the same:<br /><br />6.5mm: 154.0717 @ 100 metres, 129.852 @ 300 metres, 107.806 @ 500 metres, 78.291 @ 800 metres, 66.097@ 1000 metres<br /><br />7.62mm: 161.425 @ 100 metres, 131.084 @ 300 metres, 104.045 @ 500 metres, 69.872 @ 800 metres, 62.271@ 1000 metres<br /><br />So, we can make a GPC that outperforms the M80 ball round at ranges past 500 metres, but what does it weight?<br /><br />Unfortunately for me, I don't have access to any fancy modelling programs, and wouldn't know how to use them if I did, and I couldn't find the case weight for the 6mm SAW, so I'm going to do a bit of a dodgy.<br /><br />Lake City brass weighs 92 grains/5.961 grams (http://www.6mmbr.com/223Rem.html), with a case capacity of 30.6 grains. According to municion, the base diameter is 9.49mm (http://www.municion.org/223/223.htm). The 6mm SAW's base diameter is 10.28mm (http://www.municion.org/6Mm/6x45Saw.htm), or 7.685% larger. Scaling the case capacity of the 5.56mm up by that much gives us a case capacity of 32.952 grains, and scaling the weight up gives us a weight of 99.07 grains/6.42 grams. Now, this obviously isn't 100% accurate, just look at the differences in case capacity, so naturally I need to check this against something else.<br /><br />The 6.8 SPC is 5.435% shorter, so this increase case weight to 125.151 grains (http://68forums.com/forums/showthread.php?12757-Case-capacity-and-variances-between-the-MFR-s). Now, the base is 10.63mm in diameter (http://www.municion.org/6Mm/6_8x43Spc.htm), which is 3.293% larger than the 6mm SAW. This gives us a case weight of 121.03 and capacity of 35.588 grains.<br /><br />Since it's obvious neither method is particularly good at getting the capacity right, it's probably safe to say that neither gets the weight right, either. Still, I don't have any better way to do this, so I'm going to average the two. This gives a capacity of 34.27 grains and a weight of 110.05 grains. The capacity is pretty well spot on, so I'm going to use the weight as well. <br /><br />So, with a case weight of 7.131 grams, primer weight of .35 grams, charge weight of 1.769 grams and a projectile weight of 7 grams, we get a total of 16.25 grams for a brass cased round, or 15.787 grams with a 6.668 gram steel case. I'll just round that up to 15.8 for the sake of simplicity.Someone Elsehttps://www.blogger.com/profile/01879577725836953297noreply@blogger.comtag:blogger.com,1999:blog-5557913977913148366.post-92125341859217553042014-03-21T23:54:32.678-07:002014-03-21T23:54:32.678-07:00I could be wrong, but I don't remember anyone ...I could be wrong, but I don't remember anyone saying that the GPC would need to equal the M80 in energy, just in penetration/perforation, which means that the energy can be lower.<br /><br />In that vein, I used LoadAmmo to estimate the case capacity of a 6.5mm GPC based on the 6mm SAW, but with the neck shortened by 3mm and the shoulder length adjusted accordingly. This gave me a case capacity of approximately 34.3 grains of water.<br /><br />Next, I found a drawing of the Balle D (http://i274.photobucket.com/albums/jj263/EOD72/157_zps3a38eb39.jpg) and estimated it (http://www.geoffrey-kolbe.com/cgi-bin/drag_working.cgi?unit_length=mm.&weight_unit=grains&bullet_name=Custom+bullet&re_calculate=yes&diameter=8.325&length=39&nose=24.375&meplat=1.24875&drive_band=8.325&base_diameter=6.8&angle=4.6&boat_tail=9.335&secant_radius=&weight=199&density=8.7). This turned out pretty well okay, so I used caliber ratios to scale it down to 6.5mm (http://www.geoffrey-kolbe.com/cgi-bin/drag_working.cgi?unit_length=mm.&weight_unit=grains&bullet_name=Custom+bullet&re_calculate=yes&diameter=6.7&length=31.389&nose=19.618&meplat=1.005&drive_band=6.7&base_diameter=5.474&angle=4.6&boat_tail=7.511&secant_radius=&weight=103&density=8.7) and then adjusted it to have the same SG as the M855A1 according to another estimation, while keeping the weight at 7 grams (http://www.geoffrey-kolbe.com/cgi-bin/drag_working.cgi?unit_length=mm.&weight_unit=grains&bullet_name=Custom+bullet&re_calculate=yes&diameter=6.7&length=33&nose=19.618&meplat=1.005&drive_band=6.7&base_diameter=5.474&angle=4.6&boat_tail=7.511&secant_radius=&weight=106&density=8.6). This turns out to match your length and calculated BC pretty well, so I'm going to use the estimated BC.<br /><br />I put the bullet into LoadAmmo and found that, at just under the 62kpsi limit you've set, it's possible to get a MV of 790 m/s using 27.3 grains of AR2206, which is good, because ADI powders are well known for thermal stability, so that should lessen the chances of pressure spikes (https://www.dropbox.com/s/a4cgvwy0qh5shcw/6.5x45mm%20GPC%20%28LoadAmmo%29.png).<br /><br />(side note: it may be possible to achieve these velocities at lower pressures due to new propellant formulas and grain designs - http://www.dtic.mil/ndia/2013IMEM/W15931_Vogelsanger.pdf)<br /><br />Of course, this round now only produces 343.5 joules at 1000 metres, almost 70 joules less than the M80 ball, but what happens if you compare their ability to perforate metal?Someone Elsehttps://www.blogger.com/profile/01879577725836953297noreply@blogger.com