I've got one of the first 21sf that came out with the full 1913 picatinny rail and Amb mag release. There were problems with the mag release. They didn't make manny in that configuration. I sent it back and they replaced the lower frame with the standard gen 3 configuration I love it I haven't had anymore problems works great. I recommend it
RRA Predator Pursuit 20"
RRA Entry Tactical