375 Raptor vs 308 Winchester
- Thread starter Texian Liberty
- Start date
-
- Tags
- 308 winchester 375 raptor ar10
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.
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.
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.
Attachments
Those are some impressive loadings.
Do you have a measurement method for how high your pressure is using those cases?
It does make me wonder, seeing your results vs the factory steel head cased furry ammo, If one upsized that case even further, to 358 or maybe 375 for bullet selection, how heavy one could go with the higher pressure allowance in order to optimize for a shorter 20" barrel, like you have for that long 30" barrel. By the volume, one could expect a similar expansion rate. If your results "scaled" up with the heavier projectile, might be pretty impressive.
It's a good thing i'm not rich, I'd have too many of such projects going
I necked up around 20 for a 375 raptor AR. Lost 1 case to split neck. Have not loaded any yet
The hybrid cases have been necked up to 358 Win as I have a 358 Win... and 375 dia for fun.
But one can not run high pressure in an AR 10 much more than 62,000 to 65,000 psi.
I run the 338 RCM in an 18" AR10 at max book loads and its accurate.
The original 6.8×51 necked to 6.5 CM, .308, 358, .375.
Also use hybrid cases in 8.6 blackout to get 338 Federal high velocities... And 6mm Dasher.
Extra long 350 gr 338 Maker bore rider 6.5 twist 1886 fps in 6.5 twist, max load is 1050fps in 3 twist, which is ridiculously limited to mostly subs and copper...not the 6.5 twist, which actually makes the 8.6 a much more versatile cartridge.
The 8.6 AR 10 3 twist was scrapped as unusable for me and a bolt gun in 6.5 twist replaced it.
The 338 ARC improved 6.5 twist and tiny 338 Spectre are much more accurate with subs than the 8.6 AR10 3 twist.
Why carry a AR 10 3 twist that's less accurate and more limited than a lighter AR 15 to do the same subsonic job....your choice.
But one can not run high pressure in an AR 10 much more than 62,000 to 65,000 psi.
I run the 338 RCM in an 18" AR10 at max book loads and its accurate.
The original 6.8×51 necked to 6.5 CM, .308, 358, .375.
Also use hybrid cases in 8.6 blackout to get 338 Federal high velocities... And 6mm Dasher.
Extra long 350 gr 338 Maker bore rider 6.5 twist 1886 fps in 6.5 twist, max load is 1050fps in 3 twist, which is ridiculously limited to mostly subs and copper...not the 6.5 twist, which actually makes the 8.6 a much more versatile cartridge.
The 8.6 AR 10 3 twist was scrapped as unusable for me and a bolt gun in 6.5 twist replaced it.
The 338 ARC improved 6.5 twist and tiny 338 Spectre are much more accurate with subs than the 8.6 AR10 3 twist.
Why carry a AR 10 3 twist that's less accurate and more limited than a lighter AR 15 to do the same subsonic job....your choice.
Attachments
16" 308 6 lb 2 ioz without scope, carbon fiber, magnesium, and titanium.
Lapua brass LR or Lake City.
The 155s shown on the chronograph starting loads are 2815 fps some g1 bc's .45 to over .5
The good load Sierra Palma match at 2875 fps, from this light 16" 308...accuracy is very good.
The 168 ELDM 2756 fps 523 g1, or 208 eldm ay 2442 fps .690 bc. Most good to 1200 yds if necessary for long range shooting in a 16" 308.
The 375 Raptor is a short range thumper...
And I just ordered a 375 Raptor barrel to replace the ridiculous limiting 3 twist in 8.6 Blackout.
Which is a bolt gun now and has a 6.5 twist and is a much more versitle cartridge with better accuracy with the 6.5 twist.
Lapua brass LR or Lake City.
The 155s shown on the chronograph starting loads are 2815 fps some g1 bc's .45 to over .5
The good load Sierra Palma match at 2875 fps, from this light 16" 308...accuracy is very good.
The 168 ELDM 2756 fps 523 g1, or 208 eldm ay 2442 fps .690 bc. Most good to 1200 yds if necessary for long range shooting in a 16" 308.
The 375 Raptor is a short range thumper...
And I just ordered a 375 Raptor barrel to replace the ridiculous limiting 3 twist in 8.6 Blackout.
Which is a bolt gun now and has a 6.5 twist and is a much more versitle cartridge with better accuracy with the 6.5 twist.
Attachments
So, to challenge myself ... I'm building a 375 Raptor...the 20" long barrel is in the mail, but dies, and bullets haven't shipped yet.
Notice I'm using hybrid cases for the raptor against Lapua or LC for the 16" 308.
The 308 will have better long range the Raptor will put the short range energy on target,.... going for supersonic, I already have enough sub guns.
I already cut down and opened up the hybrid 6.8x51 cases to 375 dia. To get every advantage out of the 375 Raptor.
Notice I'm using hybrid cases for the raptor against Lapua or LC for the 16" 308.
The 308 will have better long range the Raptor will put the short range energy on target,.... going for supersonic, I already have enough sub guns.
I already cut down and opened up the hybrid 6.8x51 cases to 375 dia. To get every advantage out of the 375 Raptor.
Attachments
Have you decided on a any loads yet? I built a 16" midlength gas and have shot a total of 60 rounds. The only recipe I've tried so far is:
Starline .358 brass necked up to 375 - was an easy operation
I re-used the primers I got from decapping the hybrid cases I intend to try
35.5 grains of IMR 4198
Speer 235 semi-spitzers at a COL of 2.565 crimped
25 round average speed was 2052. These were the first through the barrel. The rifle operated perfectly with zero failures of any kind other than I noticed my optic sliding forward ever so slightly. The round is a real thumper!! I have some more 235 Speers loaded to shoot and will move to 270 grain Speer spitzer boat tails.
No it will be next week before any of the stuff arrives in the mail...then I'll start experimenting.
I made this 165 gr bullet to see how fast one can go with the 375 Raptor.
Lehigh Defense makes some 175 grain fracturing bullets that expand down to 1200 fps...but the BC is very low so maybe it's only a 250 to 300 yd bullet at most.
I have some 400 & 200 gr Maker bullets coming to play with along with the 270 gr and 235 gr from Speer & 300 gr bullets.
Maker does not have the 175 or 190 gr tipped in stock.
I'm not planning on hunting with it but should be fun for messing with.
I plan on experimenting with high velocity rounds mostly.
Attachments
The 375 raptor is intriguing in the AR10 platform, at least for me. I already have the lords caliber in 375 h&h in a m70, it’s my most carried rifle up here in AK. I might have to build one someday soon to see if the juice is worth the squeeze.
Similar performance in the lighter bullet weights to a h&h but out of a highly controllable AR platform makes for one hell of a bear fighting gun. “If” the speeds are there.
Similar performance in the lighter bullet weights to a h&h but out of a highly controllable AR platform makes for one hell of a bear fighting gun. “If” the speeds are there.
I've necked up surplus LC 7.62, Sig 277 fury hybrids and new Starline .358 Winchester. None were difficult but the 358 was the easiest. I'm currently shooting the Starline brass only in order to fireform. Water weight in the newly converted Starline brass was 53.4 while the once fired measured 53.6
I've been using GRT to find acceptable loads which for me is a load ratio of >= 90% and a burn rate of 100%. GRT indicated a number of powders that I had not seen mentioned anywhere on the web such as AA2230, N120, IMR 4227, IMR 4198, H4198.
So far, all I've tried is what I mentioned in my previous post. The simulation is telling me the best velocity I can expect from those components in my rifle would be 2155 fps using 37 grains of IMR 4198. The absolute fastest with the 235 Speer semi-spitzer would be using AA2230 for a velocity abound 2300 fps
I've been using GRT to find acceptable loads which for me is a load ratio of >= 90% and a burn rate of 100%. GRT indicated a number of powders that I had not seen mentioned anywhere on the web such as AA2230, N120, IMR 4227, IMR 4198, H4198.
So far, all I've tried is what I mentioned in my previous post. The simulation is telling me the best velocity I can expect from those components in my rifle would be 2155 fps using 37 grains of IMR 4198. The absolute fastest with the 235 Speer semi-spitzer would be using AA2230 for a velocity abound 2300 fps
I find 2500 fps available in QL predictions, with 53.6 H20 capacity. With just 60 gr H20 capacity 2600 fps appears.
Mine is a 20" barrel should arrive in a few days.
So I'll have to load and shoot it to see what case capacity I actually have, and chronograph it to see if I'm satisfied with its performance.
I'll be running most at 65,000 psi or less with hybrid cases, others depending on capacity.
I run the 18" 338 RCM in AR 10 at 65, 000 psi max. So the same will apply to the 375 Raptor.
I'm not to interested in it's sub performance but will run some Maker 400s to play with. And probably do some trick shit to run them way above sub speeds, for more lively fun.
Since ya make the brass, you can alter the chamber to gain an extra 10 grs of H20 and 2600 fps on the 235 grainers...something to consider, with a long 20" barrel, and into supers where the better killing power is at anyway.
Mine is a 20" barrel should arrive in a few days.
So I'll have to load and shoot it to see what case capacity I actually have, and chronograph it to see if I'm satisfied with its performance.
I'll be running most at 65,000 psi or less with hybrid cases, others depending on capacity.
I run the 18" 338 RCM in AR 10 at 65, 000 psi max. So the same will apply to the 375 Raptor.
I'm not to interested in it's sub performance but will run some Maker 400s to play with. And probably do some trick shit to run them way above sub speeds, for more lively fun.
Since ya make the brass, you can alter the chamber to gain an extra 10 grs of H20 and 2600 fps on the 235 grainers...something to consider, with a long 20" barrel, and into supers where the better killing power is at anyway.
New meaning to building an AR....
Got most of the parts for the 375 Raptor biuild...
I "assumed" the 3 stores who sell basic AR parts are still in business.
2 were closed, and the other was not stocking basic AR parts you had to order them.
Lots of new state laws governing guns has been passed...using the liberial courts to decide what's constitutional.
So now wait 7 to 10 days... or make and modify your own AR parts for the build.
Got the new 375 Raptor barrel...it needed some work ...
Re-crowned it in the lathe, polished the feed ramps, lapped the gas port area and complete barrel.
It's 100° and atleast 120° in the shop...lots of breaks are necessary.
Also the barrel has had a gas block mounted on it before I got the "new" barrel.
Interesting times...
Got most of the parts for the 375 Raptor biuild...
I "assumed" the 3 stores who sell basic AR parts are still in business.
2 were closed, and the other was not stocking basic AR parts you had to order them.
Lots of new state laws governing guns has been passed...using the liberial courts to decide what's constitutional.
So now wait 7 to 10 days... or make and modify your own AR parts for the build.
Got the new 375 Raptor barrel...it needed some work ...
Re-crowned it in the lathe, polished the feed ramps, lapped the gas port area and complete barrel.
It's 100° and atleast 120° in the shop...lots of breaks are necessary.
Also the barrel has had a gas block mounted on it before I got the "new" barrel.
Interesting times...
Attachments
