cookieman , the 25acp breechplug is made by precision muzzleloading. It uses a primed 25acp brass inserted into the breech plug as the primer. The great thing about this breech plug is that it has a hex nut design for installing and removing it . This makes removal a snap. Go to prbullet.com for details. I think this item made my sidekick , I would not shoot it without it