Keith said:You have to be more specific. Different powders have different burning rates. Tripple Seven for instance is a rather fast powder and will reach maximum in shorter barrels. Black Mag'3 is a fairly slow powder and will require longer barrel length to reach maximum. Black Powder is also fairly slow so the longer barrels will get higher velocity with 100gr. or higher charges. It is also somewhat dependent on the bullet construction and weight (sabots vs. conicals and light vs. heavy). You may have noticed that most "magnum" muzzleloaders have 26-27 inch barrels. I believe that the manufacturers know that with charges of 100-150 grains the shorter barrels will not use all the powder and the longer barrels are required to get any gain from the additional powder.