If they did that, sales of the M855 rounds could be restricted or banned under language in the Gun Control Act of 1968 (GCA), which limits possession of ammunition to stuff "primarily intended to be used for sporting purposes."

The ammunition guidelines in the GCA were intended for handguns, but are now being applied to ammunition used in AR-15 rifles — the semi-auto clone of the military M-16 — because AR-15 pistols use the same fodder.

("Pistols" firing .223 and Russian short aren't particularly useful as holster- or concealed-carry guns, and manufacturers were warned this was going to happen when they brought them out. Though of course no such concerns would arise if the G-men just obeyed the Second Amendment.)