jonathan1994 Posted November 26, 2018 Share Posted November 26, 2018 Reduced Power 308 for AR10 (probably not M1A, FNAR iffy since you can adjust the gas, FAL/G3 no clue) 2A arms 308 18” pencil barrel, rifle gas with SLR gas block in a heavy metal 3 gun set up with Failzero bolt. It’s not your average AR10. Everything is lightweight/polished/tuned and runs at the ragged edge of failure for low recoil, but maneuverability. This gun has shot about 1000 rounds of full powered ZQI/Perfecta junk ammo at very high rates of fire in 3 gun and play and kicks no more than a 6.8spc with a can. Its fired brass reads 0.006” – 0.011” longer than other guns fired 308brass I have. Its chamber reads at least 0.006” longer than my other 308’s based off brass fired with the gas off. I wanted to experiment with powder puff loads to extend its life and hopefully improve on the dismal 4-8 MOA accuracy. H4895 for use of the 60% rule. 125gr FB bullet. Listed Max for 125gr was 49gr. Using ZQI brass (so 2gr reduction needed). This is VERY hard brass to resize. I suspect it will be brittle and its getting stretched about 0.011” on the first shot. Factory ammo from Base to Datum Line reads 1.620 with my comparator. Yes, I suspect my Hornady comparator has a 0.010” bevel. The chamber is about 1.627 measured from brass with the gas turned off. Since I suspect 0.010 error from my gage I’m guessing it’s actually about 1.637” so only 0.003” from NoGo!!! Brass was full length resized to about 1.625. The lower pressure cases shrunk (no doubt only growing in diameter but sucking in the shoulder) and did not seal off against the shoulder as the brass came out filthy with massive deposits in the case rim and obvious gas flow marks on the body. About 42gr with ZQI brass (so 44gr with commercial) seemed to seal off. This was with the gas wide open so maybe tuning the gas would have allowed 40gr to seal off. Maybe softer brass would seal off earlier. My gun is an abnormally efficient set up, but I was amazed it cycled at only 32gr and 1848fps and kept cycling all the way up with the gas wide open. This was laughable soft. Like a 300black and there was plenty of gas driving the muzzle brake (poor, low pressure powder burn). I had the SLR 100% open so about 17 clicks, whereas factory ZQI runs at about 8 clicks. As the powder charge goes up, the brass starts growing. I’m guessing this is the result of the bolt unlocking too early (overgassed) and working the brass as the bolt opens. Ignoring the muzzle brake math puts the powder puff starting load at about triple the recoil of 223 whereas full powered ZQI 147 is 4x the recoil. Counting the muzzle brake, its only a mild difference in my gun between full power and the powder puff, but the harshness is gone from the brake and the snap in the recoil is softer. It will offer little advantage in sight movement or double taps, but I do hope to get better than my current 4-8 MOA from the light loads. More testing to come as the bag of 125gr bullets I have will probably wind this barrel up for headspace. If H4198 or some powder slightly faster than H4895 could use the 60% rule this could probably get ridiculous for low velocity/recoil. 60F Gr fps Base-Datum 30 1763 1.620 dirty 32 1848 1.620 cycled, but dirty 34 1909 1.620 cycled, but dirty 36 2075 1.620 cycled HARD, but dirty 38 2250? 1.624 cycled HARD, but dirty (velocity guess) 40 2449 1.627 cycled HARD, almost sealed (chamber length) 42 2538 1.627 cycled HARD, SEALED (chamber length) 44 2720 1.629 cycled HARD, SEALED 45 2833 1.631 cycled HARD, SEALED 46 2899 1.631 cycled HARD, SEALED So summary 308 powder puff recipe = 125gr bullet, H4895, 42gr for ZQI or LC brass (170-185gr weight) , 42 - 44gr for commercial 160gr weight brass. Open your gas block all the way. If your gun cycles, turn the gas down until you have it adjusted. Check that the brass is sealing to the chamber. If your gun does not cycle, increase powder by 1 gr increments until your gun runs. Stop at the min load (45gr) and evaluate a different powder if you can’t get function. Link to comment Share on other sites More sharing options...
Jim Watson Posted November 28, 2018 Share Posted November 28, 2018 You might look at 5744, meant for low end loads. Fast IMRs like 4198 and 3031 have been used for cast bullets at lots lighter loads than the book starting load for jacketed. The 60% rule isn't just for H4895. DuPont mentioned it for IMR 4895 a long time ago. Link to comment Share on other sites More sharing options...
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