Oops, posted the above accidentally while trying to get formatting aligned. Essentially, it seems that it's a balance between heat and powder volume. I ran both fast and slow powders at the same velocities and there seems to be little difference in calculated barrel life. The RL33 remains a mystery as to why it generates so much heat vs say Ramshot Magnum. RL33 is still slower than Magnum, and with 5gr of powder difference it's a huge difference in barrel heat. All I can attribute this to is time - that the RL33 burns so slow that there's more opportunity for heat conduction to occur. RL33 shoots very accurately, but I'm looking for an alternative which can produce the accuracy. I always let the barrel cool and never shoot the gun if it's warm to touch, but according to the Excel document, this doesn't look like it makes much of a difference between powders, and that the 264 is simply doomed. If I find that I've shot out the barrel, then a 1:8 twist will go on. Interesting stuff, thanks everyone!