I built an SBR using your RTB 4.5 barrel and bolt carrier. The barrel and a Dead Air Mask HD are tucked under an Aero Precision handgaurd.
I took it to the range today and used only 2 types of 22 ammo. Both ran great at a few failures to feed, but in all instances they happened when I was shooting fast. The nose of the bullet was tipping down in the magazine preventing it to be presented to go up the feed ramp. I'm thinking it's a mag spring issue.
Just wanted to let yall know that I'm enjoying ya'lls product.