The brace essentially replaces a buttstock, which sits at the end of most long guns, like rifles, to help absorb recoil.
The definition doesn't note anything about the length of a barrel, meaning longer pistols like the Ruger AR-556 that mirror a rifle can still be categorized as a pistol if it meets the criteria, said Rick Vasquez, a former ATF firearms enforcement officer who owns a firearms business that offers training in identifying firearms and on regulations.