There are a number of factors. Burn rate and the amount of the powder do matter. In general a 300 Winchester Mag would need a longer barrel than a .308 to reach it's peak performance.

Up to a point longer barrels increase your velocity, but shorter barrels are generally stiffer and have a higher accuracy potential. That's why you see 26" barrels on some varmint guns but the same caliber in a benchrest rifle might have a 20" barrel.

Also the very long barrels are a holdover from blackpowder days when you needed the long barrel to insure that most of your powder burnt in your barrel. There's a modern trend oa short barrels to save weight and make the rifle more compact.

Edited by - diyj98 on 01/28/2003 11:25:57