The zero tax stamp that took effect January 1 could let captive piston ammunition sell over the counter. Each round still counts as a firearm, so an FFL must run a Form 4473 and record every serial number, yet one form can cover a whole box.

A 1902 patent by J.E. Bissell showed the method in a lever-action rifle, earlier than the 1909 Maxim silencer. The Soviet PSS pistol later fired SP-4 cartridges that trap gas with an internal piston.

Reloaders might reuse the cases, and a shooter could load them into an ordinary hunting rifle when a quieter option is needed.