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I repeat. It is not the threaded hole. The grips I tried did not fit minus the screw. The receiver shank is oversized and too long. The lower portion of the grip shank would have to be ground down to fit the inside of the pistol grip. The gap between the grip and receiver is wide enough for debris to enter the safety and rear takedown pin detent holes in the receiver. Not a "cosmetic" blem. Furthermore, I purchased a complete assembled lower receiver, not a parts kit.
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It may be a combination, or one of either:
The grip slant/shank protruding too far down,
or,
The shoulders above the grip being cut too high (which would result in the same as the shank being too far down, but that may be "in spec" in size, and instead the shoulders may be cut too high).
Either way, the BCM Mod 3 worked for me (no gap). You may want to try one of those (or the Mod 0 or 1). The rear tang of the receiver on these are also cut WAY high, so beavertails do NOT mate well with them (leaves a HUGE gap between tail and receiver tang). The Mod 3 seems to have less gap there as well (perhaps on normal receivers they press in and bend into a nice tight seal?).
I'd show a pic of mine, but PB is done (no one's going to pay the "fee" to use them as 3rd party posting, much less me).