Howdy,
New to the site. R51 owner with serial # 54XX. Had a great experience with mine for the first 178 rounds fired through it and then the magazine started releasing after every round fired. Also had some FTF and a couple FTE's.
Like the gun very much and hope Remington gets it right.
Chris
Welcome to the board. There's a pin smaller of the two that's to the rear of the gun next to square QR code. That was the one I had problems with. Also the slide stop spring its easy to mess the tab on the pin. If the tab ends up on top of spring every time gun is fired the slide will lock up. I'll post when I find out when my gun will be repaired.