Was the muzzleloader that uses smokeless powder developed 20 years ago?
No, it was some 120 years ago when muzzleloaders, blackpowder cartridges, and shotguns ALL began using a propellant designed to be a better sub for blackpowder.
That included "King's Semi-Smokeless," "Lesmoke," and quickly developed from the monopoly of DuPont-- from which Hercules, Goex, and IMR were all formed.
