Q: I am having a rifle built on a Zastava M70 action in 7mm Remington Magnum. I have a Boyd laminate stock and figure the rifle will hold its zero in all weather conditions. For handiness I am thinking about having a 500mm barrel, but how much would the rifle lose in regard to velocity and trajectory? Would the 7mm Rem. Mag. still be ballistically superior to the .270 Win?
A: While the exact amount of velocity you’d lose by having the shorter barrel length will vary depending on the particular load, bore tolerance, etc, you can figure on a reduction of somewhere between 180 to 200 fps with the 7mm Rem. Mag. fired from a 500mm rather than a 600mm barrel. This is roughly comparable to the amount of loss you’d get by shortening the barrel of a .270 by the same amount. If you fired 130gn and 150gn bullets in the .270 in a 600mm barrel and 140gn and 150gn in the 7mm Rem.Mag. in a 500m barrel, I doubt there would be enough difference to notice between the two calibres. The criterion of what any 7mm Magnum will do is with a 160gn bullet at 3100 fps, so I’d advise you to get a 600mm barrel.