I opened mine up to 6.5mm-300 Win Mag
24 1/2" barrel. 1-8 twist. 80gr H870 + 140gr Accubond = 3300 FPS
The triangle group is 70gr RL25 + 140gr Accubond = 3250 FPS
Never tried Magnum & never been worried about the temp issue myself. I test when the conditions are similar to what I am going to hunt in are.