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Old March 27, 2011, 07:45 AM   #1
G-DOG58
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M1A vs HK91 ~~~~~~~ Same load???

Would a load that's good in an M1A be good for an HK91?
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Old March 27, 2011, 06:53 PM   #2
Slamfire
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I have a PTR 91 and match M1a's.

Both rifles should use powder no faster than IMR 3031 and no slower than IMR 4064 with IMR 4895/H4895/AA2495 being the "standard" propellants.


As for bullet weights, my PTR function with 150's and 174's but kicked more with the 174's. I did not like the recoil. These roller bolt actions are delayed blowbacks and I think the heavier bullet weight is harder on the system.

Loads for these gas guns are not as hot as commercial. If you are using GI or commercial ammunition made for the M14, then it should be fine in the HK91.

Keep your chamber flutes clean. These roller bolt use gas lubrication to float the upper 2/3rds of the case off the chamber walls. The bottom third is the gas seal. If the flutes gum up, excessive breech friction will result, creating failures to extract or eject.

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Old April 3, 2011, 10:19 PM   #3
Ivan
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The HK 91 isn't a gas gun. It is delayed blowback, so just about anything with a similar recoil impulse should work.

- Ivan.
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Old April 6, 2011, 07:12 AM   #4
G-DOG58
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Sounds like a ''cleaner'' powder would be more important with this rifle.....
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Old April 10, 2011, 08:05 AM   #5
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I got a load from the HKPRO site, 42 grains of IMR 4895 behind a 150 grain bullet. Shot a decent group in the HK91, the M1A didn't like it......
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Old April 10, 2011, 09:16 AM   #6
Slamfire
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Quote:
I got a load from the HKPRO site, 42 grains of IMR 4895 behind a 150 grain bullet. Shot a decent group in the HK91, the M1A didn't like it......
Forty two and a half grains of IMR 4895 is a common load with the 155 Nolser, so it may be the individual rifle.

Quote:
It is delayed blowback, so just about anything with a similar recoil impulse should work.
Slow burning powders will have excessive pressures at unlock. The extreme case is if the pressure is high enough the case will burst or separate. If that does not happen you will over accelerate the mechanism and slam/bang things up.

It is better to use faster than slower powders in these mechanisms.
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Old April 10, 2011, 09:34 PM   #7
Ivan
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Hi Slamfire,
Here is why I don't think the powder's burning rate really matters much with a roller lock gun:
The bolt and case start to move at the instant of ignition.
The fluted chamber is there because the case is expected to move while there is still pressure in the chamber.
The mass of the bolt and roller lock delay are calculated to open AFTER the bullet has left the barrel at which point the pressure is ambient.
The momentum imparted to the breech is dependent entirely on the mass and velocity of what goes out the muzzle.
There is no gas port, so it really doesn't matter what the shape of the pressure curve is as long as it doesn't exceed a maximum standard specification for chamber pressure.
As long as the weight and velocity of the bullet and the weight of the powder charge are not VERY different, the recoil impulse will be similar and the time to unlock the action will be similar.
Therefore, as long as you don't fire ammunition with grossly increased ballistics, everything should work the same.

I believe this should be same with recoil operated guns like a Pedersen or a Maxim or BMG. Think about it: When was the last time anyone was concerned about the pressure curve for something like a 9 mm handgun? As long as max pressure is not exceeded and the velocity is close, everything should work. Accuracy though is another issue entirely.

I have a couple friends with CETME rifles. Perhaps I will ask them to test with some slower powders.

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Old April 10, 2011, 09:45 PM   #8
Ivan
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Hey folks,
Don't take this the wrong way. I believe Slamfire's powder suggestions are pretty good. I don't have ANY very slow burning powders even though I should a few calibers in both semiauto and manually operated guns.

I am taking this as pretty much a theoretical and possibilities kind of discussion.

Unless you are playing with some serious large capacity magnum type rifles, medium burning rate powders should work just fine. FWIW, I use IMR 4064 in .300 Winchester Magnum with 168 Sierra HPBT. The velocity is a couple hundred FPS below where I could reach with another powder, but I don't like having the snot beat out of me and when a factory rifle shoots 1/2 MOA for 5 shot groups, I don't complain.

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