I was just watching a youtube video about a specific rifle with a 16 inch barrel. It was chambered for .308. The narrator states " the .308 cartridge needs at least 18 inches of barrel length to fully burn all the powder in the round." Is this a true statement, if so, of what kind of powder..? are there not quicker burning powders for re-loaders ( aside from the obvious pistol, shotgun, rifle, and black powder groups) ? During my life, as a child, I was very proficient in the area of re-loading .357 ammo for my dad. Since then I have done very little re-loading, but just had to ask, I'm afraid I have become spoiled in just having "Uncle Sam" supply it. I'm retired now and will be making a quick turn to doing it for myself as seeing the current cost, and quality variances in the ammo sold over the counter. Any help would be appreciated.