i was very dissappointed with the "thing" that colt was inserting with their rifles(ar15) s years ago- esnentally it was a chamber adaptor to allow 22 lr to fire in the 223 - accuracy was horrible , and it misfed most/all of the time- i didn;t know whether to blame the magazines or the adaptor- far better off getting a 10/22 (and cheaper) and doing the "heavy duty" thing to that than using that thing( properly, i guess it was a bolt carrier group) -there were two deals available at the time, either the 22 version, or a"tactical package" in 223 - scope, bayonet(m9 phobos) 2-20 rd mags, and a sling- i traded for the other when i saw such a pos it was- think it was called an achiesson adaptor at the time- and it's still a RESTRICTED - no gophering , squirreling, or rabbits-