[oldsoonershooter]

I was at a pretty large gun show it Tulsa today looking for a BCG, apparently like a lot of folks. I found one that the seller said had been an M16 version, but had had the back end modified to be open instead of completely enclosed. I ask why that was done and he responded to make it legal for use in an AR 15. I wasn't aware that there was a legal issue in using an M16 bolt in an AR 15. Does anyone know of this regulation? If so, i had better remove some of my bolts.