The newer type semi-auto lower recievers have a shelf milled into them that won't accept the S, F, A trigger groups, I think. I have an older one, made by Special Weaponsfrom a stainless steel cast reciever. These were made by Special Weapons before they sold out to Century Arms, and it is a pretty accurate rifle for it's original intended purposes. I bought the G-3 furniture as well as the telescoping butt stock for it. The nice thing about these to me, is that the magazines were very inexpensive, they are very reliable in the field conditions they were designed for, it has been accurate, and the recoil is almost nil. The ergonomics did take a little getting used to, there is no last round bolt open function, and they do dent the cases when they are ejected about 40 feet away. Once I got adjusted to the placement of the controls, it grew on me. It is fairly heavy, but it has the nickname of "The AK-47 of the full-power main battle rifle" for a reason. Mine has continued to function fine in very filty conditions. The reciever on mine has the 3 positions on the trigger group, but will only shoot semi-auto, but it shoots when placed in either position besides "SAFE". This makes it easier to go from SAFE to FIRE with my strong hand, as the safety can be pushed forward and down for fire instead of having to be pushed up and forward, which is much more difficult to do without taking my eyes off of the target. I have heard that the Century Arms CETMEs are a crap shoot, but I have been well-pleased with mine. My health is declining, so mine will be sold soon, but I had a lot of good times running her.
