Grip modules for A0 and A1 models are interchangeable and sold online. Both the slide and barrel are milled from carbon steel. The barrel has hammer-forged rifling and a muzzle threaded 1/2x28 TPI.

I [was] much astonished and shocked at this contrivance, which I afterwards learned was called the iron muzzle." Slave with Iron Muzzle is an illustration from the 1839 publication, Souvenirs d'un ...

Perhaps the most significant change introduced, compared with the standard M4 or M4-A1 shotgun ... this technology allows for up to 50% more muzzle velocity and penetration in certain cases ...