P Flados
Member
I used Quickload to figure out some stuff.
My suspicion that the allowed chamber pressure is a big input was spot on. The higher the better. As long as you are going to stay in SAAMI limits, the 65,000 psi rounds are going to win.
I also figured that fast burning is more efficient than slow burning. I was not sure if "high energy mattered, so I ran both TiteGroup (TG) and Red Dot (RD). Faster trumps high energy.
I was also correct that the heavier the bullet the better (as long as it is still accelerating when it get to the muzzle).
FYI, I knew the 308 did not stand a chance, but I ran it anyway with a normal powder. I re-did it with a 220 gr bullet and RD but it only increased to 82 ft-lbs/gr.
I also found that big cases reduce potential max efficiency. The 300 Rem Ultra Mag is higher pressure than the 308, but it maxed out at 57 ft-lbs/gr with the 220 gr bullet and RD.
Here is a summary (all with 20" barrels):
My suspicion that the allowed chamber pressure is a big input was spot on. The higher the better. As long as you are going to stay in SAAMI limits, the 65,000 psi rounds are going to win.
I also figured that fast burning is more efficient than slow burning. I was not sure if "high energy mattered, so I ran both TiteGroup (TG) and Red Dot (RD). Faster trumps high energy.
I was also correct that the heavier the bullet the better (as long as it is still accelerating when it get to the muzzle).
FYI, I knew the 308 did not stand a chance, but I ran it anyway with a normal powder. I re-did it with a 220 gr bullet and RD but it only increased to 82 ft-lbs/gr.
I also found that big cases reduce potential max efficiency. The 300 Rem Ultra Mag is higher pressure than the 308, but it maxed out at 57 ft-lbs/gr with the 220 gr bullet and RD.
Here is a summary (all with 20" barrels):
Code:
Gun 308 454 454 454 454 308 300RUM
Bullet (grs) 150 175 255 255 405 220 220
Powder H335 TG TG RD RD RD RD
Charge (grs) 49.8 19.53 16.52 15.41 8.69 17.86 38.1
Energy (ft-lbs) 2779 1828 1639 1679 1084 1467 2184
Energy/gr (ft-lbs/gr) 55.8 93.6 99.2 109 125 82 57