Answered some of my questions on the two AR10 savage rifles I had, they went with the shorter version of the upper and lower and although probably not a bad design savage had in issue with the proper timing of the BCG action during a reload causing the the bolt lugs to slam into the barrel lugs before lock up and damaging the bolt lugs. They were great shooting rifles and beautiful rifles to look at but just not good for long term use when having to replace the bolt every 500 or so rounds.