I belive that most of them fit. I have heard SOME may require fitting but I have not seen any that require it. I think the idea of the G2 is just to be a better Contender. I have a G2 and an older custom SSK Bbl. in .358jdj(frome 1986 I think) and it fits realy well on my G2. If you are concerned about a particular bbl. contact T/C.