Speaking as an LEO, I can tell you that it is correct that the huge majority of us don't know anyting about 922r. I expect those few that do are probalby fellow gun nuts and therefore don't care that the gun might not technically be compliant. The obvious exception would be some feds charged with enforcing those laws.
At least in NC and VA (the two states I have experience as a LEO in), we can't enforce federal laws anyway, so long as the gun is legal under state law, there is nothing much we could do even if we wanted to.
