I feel lucky and quite foolish.
I recently purchased a Masterpiece 9mm with a hellfire trigger. Shot 150 round last week and never got it to engage. I did some reading and went back out yesterday. I change my left hand position from gripping under the barrell to placing the left hand on top of the barrell. Well. It worked. Unfortunately, when it went full auto, Mr. Dumb Butt here wasn't ready. My left hand was thrown in front of the barrel. It blew a hole and broke my left thumb. I'm seeing a surgeon on Monday. It could have been a lot worse. Lesson learned.