Did the length of the 129AH create any compressed loads?Pressure Test on 129 gr. Absolute in 6.5 PRC. As always your mileage will vary. Start low and work up.
Weather thin overcast with 55-58 degrees. Humidity was around 35%.
Tikka Action - modified for long cartridge operation
Barrel: Proof Research Carbon barrel w/7.5 twist and 22" length
Brass: ADG, sized with 0.288 bushing (no expander ball)
Primer: Federal 210 Std. Large Rifle
COAL: 2.955" - not that it really matters with this bullet
Process: I loaded up 2 casings with same amount of powder, then increased in half grain increments. The 59.0 grain loads may have been mildly compressed. The bullets were seated deeply with the first drive band just visible at the neck. I continued until the first signs of sticky bolt lift, then backed off one full grain and called it my Max load.
Starting load: 55.0 gr. Ave. velocity 2,934 fps
Max load: 59.0 gr. Ave. velocity 3,095 fps *
* This was the highest load I had prepared. I did not reach any pressure cut off, so could have gone a little higher. No signs of pressure with 59.0 gr. of H4831 SC.
IMR 4451 (Close in burn rate to H4350)
Starting load: 56.0 gr. Ave. velocity 3,118 fps
Max load: 58.0 gr. Ave. velocity 3,255
I did shoot the 58.5 and 59.0 gr. loads as well. At 58.5 I got a big jump in velocity (3,317 average) indicating I was hitting the pressure ceiling. The 59.0 gr. load resulted in a very slight, but sticky bolt with ave. velocity of 3,326 indicating the max velocity curve was flattening out.