Wednesday, April 8, 2009

More NATO Round Selection Ponderings

I was thinking about an alternate universe in a previous post. One where MacArthur's accepts the .276 Pedersen and switches from the .30-06 for the then-new .276, and obviating the need for a .280 British, the .308 Winchester, and the .223. I thought that alternate universe might have a better outlook on military rifle ammunition than the world we live in now. The .276 would be better than the silly .223, but easier to field than the .30 caliber types.

But then I remembered that those calibers are just bullet diameters. What if the length was all wrong? I had no idea if that .276 was as long and as relatively unwieldy as a .30-06 and thus not ideal for shorter stroke actions. That and whether the Brit .280 might be a great improvement over the Pedersen, perhaps introducing a rivalry and the confusion of a possible switch. So I did some checking...

My fears were unfounded.

From left to right: 6mm SAW, 6.5 Grendel, 6.8 SPC, 7mm Bench Rest, .280/30 British, 7mm-08, 7mm Second Optimum (Liviano), .276 Pedersen, .308x1.75", 7.62x51 NATO. (from wikimedia commons.)
Here are the rounds I was thinking about for internal comparison, in order of length:
As you can see, the .308, .276, and .280 are almost identical in length. I bet the 2 skinnier rounds had really nice flat trajectories. The .276 Pedersen shot 140 grain projectiles 2400 fps in the 1920, while the .280 was getting similar performance, maybe a touch more, with the same weight 30 years later. My guess is they were nearly identical in performance, and if the .276 was widespread, no one would have bothered with the effort to bring about a .280, later.

The .308 was also about the same speed, add maybe 300 fps, with a 150 grain bullet. With a harder to carry cartridge.

The .223 is over 3000 feet per second speed with a 60 grain bullet. A much different cartridge, clearly.

So unless there was something ballisticallly unsound about the .276, we might still be fielding it pretty universally today, in the US and throughout NATO type allies. Snipers might need a bit more oomph, so the .30-06 might still be around and used in the army, too. These 7mm bullets are rifle bullet, or a carbine bullet? Dunno. I'd need 70 years of field testing to really have a light on that, with no one with a memory of a REAL rifle bullet in battle to properly compare. The same way we didn't have many veterans that fought with the .45-70 Gov't survive until WWII to talk about what a pea shooter the .30-06 was.

What do I mean by 'ballistically unsound?' Heck if I know. I do know that if the bullet is a certain weight and shape for the powder charge, and rifling ratio, and number of grooves and lands, and many OTHER factors, it will 'fly' better, and that deviating one of the many variables can give the bullet a propesity to tumble or yaw. I have to assume that smarter men than me considered all that with ALL the tests of possible new calibers, and, again, there was no real difference in performance between the Pedersen and Brit 7mm rounds. I know that .223 round was tweaked in the late 70's early 80's to get better performance, so cartridge change does happen. (Shoot the .30-06 is a ballistic improvement of the earlier model .30-03.) But you can't get the magic big-bullet performance from a small bullet. The .223 certainly works, but so do Volkswagons. Doesn't mean I want to shoot one or drive the other. Or drive one or shoot the other.

And there is always the chance that someone with much more knowledge that me will see where I took huge leaps of faith on false assumptions and can point out where my 'conclusions' from muddle headed theories and contrafactual data made me go way off the sound-ballistics reservation.

(Hmmm, being almost identical to the .308 except for the diameter of the round being .62 mm narrower, I wonder if the Pedersen would kick as much in an M14? Maybe we did need that .223. Dangit!)


Tam said...

I need to get you and Dr. Strangegun together in the same room, just to watch y'all geek out.

John Moses Browning would be proud.

And, yes, that's a compliment. :)

Noah Sachs said...

What if you had a bullet with a 1 inch diameter with a flatter trajectory than a .308, and the recoil of a 5.56mm, the penetration of .338 Lapua, but the cycle on the action was very long and therefore very slow?

YIH said...

Why do you not have enough ammo?
You should be ashamed of yourself.
You need more ammo.

tsquared said...

I do not shoot any long range any more. I was never very happy with .223/5.56 in a rifle except for plinking. A long shot for me is 300-350 meters with most shots being under 100m. My primary AR's are in 6.8SPC and 9mm. The 6.8 can handle any rifle requirements from varmints to elk as I have a 115gr bullet traveling at 2500fps on a fairly flat trajectory. The AR9 can make nice little holes in paper grouped very tightly together and makes it a bit less expensive plinking.