I made up a batch of these muzzles the other day, and still have two that are looking for good homes.
They fit the Rob Allen aluminum barrels, and are mostly intended for people who want to use that barrel to build a hybrid gun. The material is black Delrin, with a 316 stainless line pin and anchor. Each of the 9/16" diameter band holes is staggered 1/8" higher than the next hole.
They are $50 each, which includes Priority Mail shipping.
email is: jdd@eatel.net