As I said before Bushmaster buys parts from military suppliers, of course the fire control parts are of the ar15 variety. They are made on the same machinery with same metal. Now with that said I hear that there are some parts made out of country that some importers are importing which is crap. I don't think either BM or Armalite put these parts on there rifles or offer the same for sale, it just would not be good for business. I have bought parts at a gun show that were crap-maybe out of spec military rejects or imports. I have seen both style of trigger gaurds on military issue rifles. The military puts out specs that have to be met. To the trigger gaurd it must be a certain color and maybe have a certain bursting or breaking point and maybe withstand so many hours is salt bath without failing. Other parts must pass a tolerence inspection with limits and a hardness spec too-besisdes a finish test and other tests. The first SGW kit I had contained M16 fire controls which I ditched because they were crap. The next hammer I got from SGW had the auto sear hook cut off of it. It is hard to tell the good parts from the bad because of the finish the part look like new although it maybe out of spec. Buy from a good known source and you want go wrong. If you purchase parts through a dealer that comes from a military contractor, chances are pretty good that the parts will be good. As for the barell lined vrs unlined, what a hot potatoe. Military uses lined, I have both, and cannot tell the difference the way I shoot. This debate on bbls will always be ongoing. Amos