You're all forgeting something ! The loss per inch of barrel depends on the initial velocity. The higher the intitial velocity the more is lost when you cut the barrel .A velocity of 3500 fps will be reduced significantly when you cut the barrel a few inches . A 45-70 velocity reduction will be negligible. I cut my 1885 Browning , 45-70 ,from 28" to 22" and didn't worry about it knowing the losses would be insignificant !!