They are ballistic twins. Use the right bullet in either and no bear will know the difference. It is best to compare sectional densities rather than bullet weight or diameter. A 140 gr 7mm bullet will do anything a 165 gr 308 bullet will do. a 160 gr 7mm bullet will perform exactly like a 180 gr .308 bullet on game and a 175 gr 7mm bullet is comparable to a 200 gr .308 bullet.