I just came across this video by chance. It shows real-time and slow-motion footage of both SMG's in full auto fire. Before watching it, I expected the B&T to clearly win with its internal recoil buffer, but it's not so clear by the video. Maybe the slower rate of fire of the H&K? The B&T definately pushed him back more than the H&K, but the H&K sorta seemed to bounce around more than the B&T. Regardless, both muzzles seemed to stay fairly in line with the target. I have a USC45 to UMP45 conversion and never found the recoil to be as bad as some have mentioned, to include semi-auto rapid fire. Full auto may be a different story. Larry Vickers did a video with a real one that was clearly hard to keep rounds on center mass with full auto. No vertical grip though. He agreed that 2-shot burst was the way to go.

I have a APC45 and a USC to UMP conversion and the UMP is dog shit compared to the APC (or pretty much any other PCC I own). Only reason I keep the UMP is because I am an HK Fanboy, otherwise itd have been sold before I even converted it. Obviously these are both semi.

Yeah, most seem to either love or hate the UMP's. I enjoy shooting mine suppressed for single and double taps. But it's clearly not a smooth shooter like an MP5 or APC9.