Okay I understand some barrels are faster and/or slower than others all other factors being equal. I have recently been wondering if the method of rifling can affect speed/friction of the projectile. When we compare hammer forged rifling to say button rifling it looks much rougher as if there would be more friction and thus produce a slower moving projectile. Button rifling in contrast looks to me anyway much smoother, hence less friction. Is this true or doesn't it make any difference?