Re: looking for thoughts on 5.56 bolt group
I agree with most of the comments. My first choices would be BCM, LMT, Colt and DD but there are several MP tested bolts that should work. I have personal experience with BCM, LMT and Colt. I know several people who run DD's and are happy.
I have heard great things about fail zero, but have never tried one personally. One of their reps at SHOT claimed to have put 60K rounds through his personal rifle with one of their BCG's without any lube and still hadn't experienced any failures. Take that with a grain of salt, but there are a lot of others saying good things about them as well. Since you mentioned "fairly cheap", fail zero may be out of the question.
trident1982- thanks for the pics