The specific lower I mounted this one on is a Bushmaster, but it sat equally well on my Colt 6920 lower as well as my Bravo Company lower.
Thanks. Thread jack- My last build was a spikes lower and PSA upper and it had a noticeable gap but it didn't have wobble or play. I handled a friends dedicated 9mm lower and the fit to the upper even with an accuwedge wasn't acceptable for me. The gap was double what mine is on the last build.