Once immediately before re-barreling a 7mm Weatherby I cut it from 26 inches to 24 inches, then to 22 inches. Starting with a 160 grain bullet at 3100 fps there was an 80 fps velocity loss for each 2 inches of barrel length. I don't think a .270 would be all that much different. I have rifles with short and long barrels and think bigger advantages of a longer barrels are better balance for offhand shooting and a little less muzzle blast. - DON