mathman
Did some quick figuring from the 7th Nosler Reloading Guide.
7mmMag 160 gr bullets 24" barrel
6 powders gave velocities ranging from 3008-3077 fps
Average vel was 3045 fps
280 AI 160 gr bullets 26" barrel
7 powders velocities ranging from 3002-3045 fps
Average vel was 3022 fps
Subtracting 50 fps for the 2" longer barrel = average vel of 2972
using MD's 1/4 rule - 1/4 of 7.5% (greater capacity of JRS than 280AI) = 1.875% or 0.01875
thus 2972 x 1.01875= 3027.7 fps for the 7 JRS.
Just math but seems like it could come real close to 7mm Mag velocities with 160 grain bullets at reasonable pressures.
