Friday, November 30, 2012
Case Taper in Military Cartridges
I was trying to determine how much case taper was appropriate for military cartridges, but the current standard seems to be "take 5.56/7.62 and copy the taper". Curious as to what effects this method might be having on ammunition design, I did some calculations of my own. What follows is the case taper, in radians, of some of the most popular military rifle cartridges, and some important experimental cartridges, putting an emphasis on those designed prior to WWII.
All data comes from municion.org, calculations done by me.
Case Taper of Various Cartridges:
.30-40 Krag: 41.22 Taper Length, .52 Taper Width, .013 Rads Taper
6mm Lee Navy: 40.70 Taper Length, .61 Taper Width, .015 Rads Taper
.30-06: 46.33 Taper Length, .38 Taper Width, .008 Rads Taper
.276 Pedersen: 37.26 Taper Length, .82 Taper Width, .022 Rads Taper
.270 Sidewinder: ? Taper Length, ? Taper Width, .013 Rads Taper
7.62 NATO: 35.77 Taper Length, .21 Taper Width, .006 Rads Taper
5.56 NATO: 33.39 Taper Length, .29 Taper Width, .009 Rads Taper
.300 Winchester Magnum: 50.19 Taper Length, .31 Taper Width, .006 Rads Taper
6mm SAW: 28.36 Taper Length, .25 Taper Width, .009 Rads Taper
6mm PPC: 23.80 Taper Length, .20 Taper Width, .009 Rads Taper
6mm BR: 23.45 Taper Length, .17 Taper Width, .007 Rads Taper
6.8 SPC: 30.05 Taper Length, .25 Taper Width, .008 Rads Taper
6.5 Grendel: 25.60 Taper Length, .14 Taper Width, .005 Rads Taper
7x46mm UIAC: 25.4 Taper Length, .23 Taper Width, .009 Rads Taper
.303 British: 43.84 Taper Length, .75 Taper Width, .017 Rads Taper
.280/30 British: 26.65 Taper Length, .32 Taper Width, .012 Rads Taper
8mm Lebel: 35.00 Taper Length, .96 Taper Width, .027 Rads Taper
7.5x54 MAS: 39.50 Taper Length, .44 Taper Width, .011 Rads Taper
7.92x57: 43.01 Taper Length, .50 Taper Width, .012 Rads Taper
7.92x33: 20.14 Taper Length, .26 Taper Width, .013 Rads Taper
6.5x52 Carcano: 41.00 Taper Length, .28 Taper Width, .007 Rads Taper
8x50R Mannlicher: 36.77 Taper Length, .24 Taper Width, .006 Rads Taper
6.5x54 Mannlicher-Schoenauer: 41.70 Taper Length, .36 Taper Width, .009 Rads Taper
7.62x45 Czech: 32.2 Taper Length, .43 Taper Width, .013 Rads Taper
6.5x55 Swedish: 40.24 Taper Length, .58 Taper Width, .014 Rads Taper
7.5x55 Swiss: 41.12 Taper Length, .51 Taper Width, .012 Rads Taper
6.5x50SR Arisaka: 36.30 Taper Length, .59 Taper Width, .017 Rads Taper
7.7x58 Arisaka: 43.93 Taper Length, .49 Taper Width, .011 Rads Taper
7x57 Mauser: 40.8 Taper Length, .55 Taper Width, .013 Rads Taper
7.62x54R: 38.10 Taper Length, .38 Taper Width, .010 Rads Taper
7.62x39: 27.3 Taper Length, .62 Taper Width, .023 Rads Taper
5.45x39: 26.80 Taper Length, .375 Taper Width, .014 Rads Taper
9x39: 27.49 Taper Length, .34 Taper Width, .012 Rads Taper
5.8x42: 30.27 Taper Length, .53 Taper Width, .017 Rads Taper
The trend revealed here is that, starting with the US .30-06 cartridge (and ignoring the experimental .276 Pedersen), American rifle cartridges have much less case taper than cartridges designed elsewhere. In fact, at the time it was designed, the .30-06 was criticized for being too much like a match cartridge, being too powerful, and in general being an overreaction to the 7mm Mauser.
As you can see, the venerable .30-06 Springfield has case taper comparable to modern benchrest cartridges, like the 6mm PPC and 6mm BR. The 7.62 NATO has even less case taper, while the .223 Remington/5.56 NATO is somewhat less severe in that respect (remember this the next time some .308 fanboy goes on about how the military adopted a benchrest/varminting cartridge).
Nearly every other foreign military rifle cartridge that saw major service had at least 25% more case taper than the .30-06 Springfield, with the oddball exceptions of the 8mm Mannlicher and 6.5x52mm Carcano.
Given only cartridges designed by foreign militaries after 1945, we can see that case taper has not deviated much from the pre-war standard. Even after the case taper of the 7.62x39 was judged too extreme in the search for its replacement, the cartridges that followed exhibited significantly more case taper than even the 7.62x54R.
Now, no conclusions can be drawn from this. However, suspicions definitely arise concerning the suitability of .008 radian and steeper case taper for military cartridges. The soundness of the design of the .30-06 cartridge is in question, and, though testing would be required to determine if its taper were too severe, the cartridge smacks of something designed as a kneejerk reaction to the much more efficient 7mm Mauser. Almost two decades later, a shorter cartridge with greater taper, much lower recoil, and much less severe bolt thrust and with almost equivalent trajectory and range to M1 Ball was developed in the .276 Pedersen cartridge.
Given that, except in legacy applications, the Russians have abandoned any taper more extreme than .012 radians, and the newest Chinese cartridge has taper of more than .017 radians, it is clear that American case taper standards are overdue for a review. What sort of results might a comprehensive test of case taper turn up? Have American cartridges been inheriting a design flaw present for the past 109 years?