375 Raptor vs 308 Winchester

[wvfarrier]

It appears the 375raptor web page is now disabled

 

[b6graham]

works for me

 

[SAUMuvabitch]

 

[PoetsRevenge]

After running the ballistics calculator a big red flag showed up (honestly it was there staring me in the face the whole time). The 375 Raptor wallops at 3,173 ft-lb @ 100 yds, while the 308 Winchester hits at 2,365 ft-lb. That's over 800 ft-lb of difference from a 48% bigger bullet using the same parent casing (only smaller), about the same powder, and a 2" barrel length disadvantage. How????

If anybody has answers I'm all ears. I want to believe you can get this kind of power out of a short action / AR10 platform. But reality is hard to ignore. Where did all that extra energy come from? Raptor chamber pressures are not supposed to be any higher than 308 Winchester, so it ain't that.

I'm going to keep this somewhat simple, as I doubt you want to dig too far into physics for your understanding of this.

You are ignoring area.
Most importantly the "piston" area that is the back of the projectile.

Peak pressure is a engineered limit of the action and components. Powder volume is a limit to total amount of fuel available. If you limit the two, then the best performance you can get out of a given pressure depends highly on the piston area. A .375 diameter piston has about ".05519531" square inches of piston area. A .308 projectile has about ".03723412" square inches. or a ratio of 1.4824 : 1

PRESSURE is a unit of force PER area. So at the same given pressure, the raptor will have almost 1.5x's the acceleration force to work with.

Now as you accelerate down the bore, the volume INCREASES at a greater rate with a larger bore. So a larger bore will drop pressure "faster" once all the fuel is consumed. With both rounds, a typical load will hover around 40 "grains" of fuel. When you're talking a short barrel, such as 16 inches. The raptor can keep peak pressure for some of that length, and still hold about 70-80% depending on loading to about 10 inches. Due to the volume increase, and the powder being "done" burning somewhere around that point, pressure will drop. someone else can punch it into quickload to give you more exact numbers but I would assume by 16" pressure is down in the 10k range. Your AVERAGE pressure over that 16" stroke however, is still pretty close to the 16" barrel for a 308, yet that almost 1.5:1 area advantage means the WORK performed is almost 50% more.

Your "limitation" starts happening as you go longer. A .375's pressure falls faster after that length. By 20 inches of barrel, a 308 is still making significant gains, where the .375 gains are minimal "per inch" longer. At 26" of barrel, a 308 has fallen off the same way a raptor has on a 18" barrel, and you've gained "about" all you can get out of the powder load.

So could one get the same total power out of a 308? possibly. Friction on the longer barrel will hurt a good amount, dropping the net gain as you get past 24" or so into barely double digits per inch longer. So while you might possibly be able to run a lighter but similar bc in the 308 and get the same total energy + range, it would take a pretty good projectile and a MUCH LONGER barrel to do it.

It works out that for any given powder load, and a target weight, and target velocity, one can optimize a barrel length and caliber. For the same parent case/volume larger caliber does better in shorter barrels, smaller needs longer. But for the same given powder load smaller can reach higher velocities, due to less weight for the same given BC. It all boils down to "how much" projectile do you need for the intended target, then how far is your max intended range, that tells you a total bc, energy needed, and weight, then you can optimize a given length (stoke) vs caliber (bore) to consume the fuel.

in short, there's no magic going on. The math can and does check out. I run a 358 winchester, which is almost identical to 308 in every way, except in comparison, my 358 shoots a 220 grain from a 16 inch barrel, at the same speed the 308 shoots a 168 from a 16 inch. From the my 20 inch and 24 308, 178 grain and 185 grain projectiles out RANGE the 358 winchester when you start talking 600+ yards. My 6.5 with again the exact same case and powder quantity, out ranges all of the above, with a lighter bullet (140-range) with similar b.c. by a huge margin, it just needs 22" of barrel to do it, and has far less impact force under 200 yards.

 

[45-90]

308 Win hybrid case 174 ELD-VT 3139 fps 3806 ft/lbs of muzzle energy.
1000yds 1720 fps 1143 ft/lbs.
22.4 MOA drop 64.6 " drift in 10 mph cross wind.
Mag length, for detachable MDT mags.

The rifle has a 30" 8 twist heavy palma, in aluminum chassis. Set up for heavy bullets 200 gr SMK to 250 Atips
Just shot the new 174 gr ELD-VT bullets today.

 

[45-90]

Also today fired the world's fastest 338 ARC imp ammo 3760 fps.
In a 16" AR 15.