Loads for Semi auto different than bolt?

[Joshboyfutre]

I'm getting ready to do some load testing for a C-308. Its basically a PTR/HK 91 w/a 16" 1:10 twist barrel. Hodgdon lists 47.7 max, planning on loading 43.0 - 47.5 in .5 increments. Only reservations I have is having seen "service rifle" loads in manuals that lists lower min/max numbers. Any input is appreciated, thanks.

 

[GooseGestapo]

Garands and M1A's are sensitive to propellant burn rate and maximum pressure. Most newer designs are more tolerant of longer pressure curves and maximum pressures.

Bolt actions aren't so constrained.
However, treating your PTR/HK as a "service rifle" will ensure its longevity.
No point in trying to "magumize" your service rifle, as it was intended to fire "service level" ammo.
After acquiring two M1's and an '03-A3, I quit loading bullets heavier than 168gr or powders other than H4895 in the .30-06. 2,800fps with a 150, or 2,700with a 165gr actually is "enough". No point in "gilding the Lily". Bullet impacts match sights, too.

 

[Joshboyfutre]

Forgot to see what weight unloading they are Hornady 150 grain FMJ

 

[Bart B.]

There is no difference in peak pressure specs for safety across all rifles chambered for a given cartridge. The commercial (SAAMI) and arsenal (MIL SPEC) peak pressure for the 30-06 round is 50,000 cup. The arsenal spec for 7.62 NATO is also 50,000 cup; 2000 cup less than its commercial sibling, the 308 Winchester. That's an insignificant amount as over half the rounds of each will overlap due to the several thousand psi spread.

There are pressure curve considerations for gas port pressure in gas operated rifle actions. You can use IMR4895 in M1 and M1A rifles with 190 grain bullets very safely, but the compromise is somewhat lower velocities. 180 grain bullets have been used with maximum charges of IMR powders 4895 and 4064 safely with excellent accuracy in both rifles. The arsenal match and sniper bullet for both rifles weighs 173 grains.

 

[243winxb]

"service rifle" loads in manuals that lists lower min/max numbers.

I think i would follow that load data. Sierra- http://www.exteriorballistics.com/reloadbasics/gasgunreload.cfm

 

[Joshboyfutre]

Excellent! I just wated to check, I've never loaded ammo for this Rifle because it destroys brass, but I'd like to see if I can get it to shoot some good groups, I've only shot cheap milsurp ammo out of it and it shoots 2-3 inch groups w/that stuff. Figure I can start using my old brass from my bolt action to make up some better ammo! Thanks

 

[Bart B.]

Only reservations I have is having seen "service rifle" loads in manuals that lists lower min/max numbers. Any input is appreciated, thanks.

That's normal because most people creating load data are ignorant about peak pressure specs being the same for both service and commercial rifles. They usually don't explain the pressure curve issues required for gas operated systems compared to manually operated ones. The proof load pressures for both are the same.

7.62 NATO Garands digested 190's over 44 grains of IMR4320 easily; M14's and M1A's couldn't.

Keep in mind the fact that reloaded cases fired in these rifles have never shot bullets as accurate as new cases.

 

[Joshboyfutre]

Yeah for this particular trip since I'm testing loads I want to head and bought some Winchester brass but I have a bunch of brass laying around from my bolt rifle that is still good that I just bought new brass though.

So when they're talking about service rifles they're basically just talking about M1A1, that wouldn't apply to any of the 91 type rifles or AR-10 type rifles? Why the hell don't they just say M1A1 instead of service rifle LOL

 

[243winxb]

Applies to all auto rifles. Not just M1.
1 slam-fire from high primer.
2 Primer Sensitivity
3 Full length sizing is the only option .
4 Powder selection for gas-operated service rifles is considerably more limited than for bolt actions of the same caliber.
5. Neck Tension, bullet movement as the round slams into the chamber.

 

[Bart B.]

So when they're talking about service rifles they're basically just talking about M1A1, that wouldn't apply to any of the 91 type rifles or AR-10 type rifles? Why the hell don't they just say M1A1 instead of service rifle LOL

Is the M1A1 30 caliber carbine the service rifle you're referring to?

The NRA has defined the AR10 a service rifle for competition; thanks to the US Army's reasoning and polite requests about 6 years ago. They had no more M14 National Match rifles to compete against 7.62 NATO Garands and M1A's in long range service rifle matches. Their best 22 caliber M16 and commercial AR equals were not accurate enough past 600 yards.

 

[Joshboyfutre]

I just meant as far as some of these reloading manuals "service rifle" loads. It seems like it's basically just in reference to the M1A1/M-14 as the AR 10 and HK/PTR rifles can handle max loadings. I see what your saying though.
Does the term "service rifle" only refer to full size rifles? By that I mean when someone refers to a "battle Rifle" they are talking about 7.62×51 and not 5.56×45 or 7.62×39. Basically would a my C308 be considered a "service rifle" but my AR would not. No real reason other than curiosity makes me wonder.

 

[243winxb]

I think service rifle is the one issued to our troops. Current is m16/AR types in 5.56

Your C308 would not be a true service rifle. I may be wrong.?

 

[mdi]

For Bart. I've had mu Garand, 30-06 for only about 5 years. Before I got it I read/researched quite a bit on load datta for the gas system. Everywhere I read, every recommendation had a give "range" of powder speeds and conservative load data to prevent damage to the operating system (most commonly bent op-rods). My Hornady manual has a section devoted to the M1 Garand loads and most are much lower than factory "normal" 30-06 loads. I understand the "requirement" for a "Garand load" is the peak pressure and gas volume at the gas port to be enough to consistently operate the action without being high enough to damage parts. Every load I assemble for my Garand is less that 2800 fps, mostly running around 2600 with 150 gr bullets. So, not challenging you, but I'm confused by your comments...

 

[Sunray]

"...they're talking about service rifles they're..." Nope. M1 Rifles, M-14 style rifles and any bolt action battle rifle. Your HK with it's short barrel is never going to give full 7.62Nato velocity. That'd be a 147 grain bullet at ~ 2733 fps.
Lot of manuals give lower powders charges for "service rifles" due to the number of 'em out there in questionable condition. And the rifles that have been converted to .308 that probably shouldn't have been.
"...planning on loading 43.0 - 47.5 in .5 increments..." The powder is kind of important. 47.7(C) is for IMR4064. That'd do nicely. You do not have to stop at 47.5 though. BL-C(2) is a good .308/7.62 powder as well.
"...mostly running around 2600 with 150 gr bullets..." That'd be close to .30 M1 ammo spec except that stuff(that theM1 Rifle was deigned around) used a 174.5 grain bullet at 2640 fps. 2800 fps is .30 M2/AP velocity.