Because the ballistics calculator as you are referring to is specifically for "exterior" ballistics, which is everything that happens AFTER the bullet leaves the barrel. The only thing that software cares about is the velocity of the bullet just as it leaves the barrel (muzzle velocity). It can care less HOW that velocity was acheived. Everything that happens inside of the action/chamber/barrel is known as "Internal Ballistics". (Everything that happens once the bullet hits the target is known as "Terminal Ballistics"). So, the fact that muzzle length effects the velocity of the bullet as it leaves the barrel is all a part of the internal ballistics calculations. Yes, UP TO A POINT, increasing the length of your barrel will increase your muzzle velocity. (That point is well beyond the practical length of a rifle).We7det_el_qetal_ra3d said:If added barrel length increases muzzle velocity, then how come most ballistic calculators on the net don't use that parameter in their calculations?