ATF Ruling In 1998 On Modern Muzzleloading Rifles:
 Black Powder, Muzzle loading weapons with "in line" firing mechanisms designed or redesigned to use modern conventional firearm primers do not meet the definition of antique firearms and are subject to regulation as a firearm. Modern centerfire primers are not an antique ignition system and are ammunition for firearms subject to regulation.

Modern Magnum Muzzleloading Rifle:
 The modern magnum muzzleloading rifle will be of a inline, modern primer design and will be loaded from the muzzle end of the barrel with the use of a black powder substitute for a reliable propellant charge such as triple seven, pyrodex or blackhorn 209 and is typically limited to a maximum safe charge of 150 grains of pelletized substitute powder of which, full potential of this powder charge can not be realized in a rifle barrel that is shorter than 26 inches long.

 A further statement is needed here on loose powder charges of granular powders, because of the difference in burn times of these powders only 100 - 120 grains of granular powder are needed for efficient velocity increase after that the powder is usually wasted as it will not be fully burned in the barrel. These rifles work best with a scope mounted usually 1.8 to 2.0 inches above the bore-line and will have a Maximum Point Blank Range of two hundred yards when set up correctly with a 1 in 28 inch twist barrel.