Yesterday, I swapped the comp over to my 16" Spike's Tactical 5.45x39mm upper, and today I took it out to do some shooting. Unfortunately, all is still not well. The comp shoved the muzzle down hard and to the left. I also couldn't get the tip of my pull-through cleaning rod out through the end of the comp. No flash that I noticed, though.
The Rainer XTC did fare much better. While I had the barrel vice blocks out, I put the XTC on my LMT 16" M4gery Although there is a bit of concussion, there was no tuning fork "ting," and not too much muzzle lift. Unfortunately, I had another Tula steel shell case get stuck hard in the chamber, cutting short that shooting session. Even if I had a cleaning rod, it took a half dozen hard hits with a dead-blow hammer to remove it.