I helped a friend build one, and he really likes his.
We did not have any feeding issues, with either the
upper, or the magazine, he had(C-Products IIRC). I helped
him develop some 123 gr. VMax loads for his, and we shot
some .5 MOA groups with it.
When I decided to get an AR-15, in something bigger than
223 Rem/5.56 Nato, I went with the 6.8 SPC, and I actually
had more problems with that, than the 7.62x39 rifle we
built. I do have the 6.8 SPC running like a top now,
and last weekend, it put 110 gr. VMax bullets into 2 for
2 sub MOA groups, with the third powder I tried for load
development. It is looking like the local coyote population
is in for a tough winter.
Squeeze