You're right, I wasn't clear on that. The top/back cuts are for clearance in the back of the BC slot near the spring pocket. The slot/hammer can also be an issue. I haven't seen much attention given to locating the bracket. The location on one drawing for the bracket rivet came up short of getting the 5.7" from the back of rcvr to pak mtg pin given on the hand sketch. That bracket also controls if it will fit in the ground mount properly.
One of my other replies shows the missing radius on the BRP BC lugs. This can give an intermittent "in battery" position which the bigger spring would affect.
2 Blanks boom, then nothing, nothing, nothing
Re: 2 Blanks boom, then nothing, nothing, nothing
Well, not sure how missed it, but looks like the top of the hammer was striking/dragging across the ceiling of the carrier. Removed a bit off the top and is now making a much cleaner clank when hammer closes on pin. Need to test to be sure.