I just broke-in a brand-new XCR-M keymod rifle, and the release lock for the receiver needed to be pulled into place after oiling. It was about a 1/4" forward from locked position. Shot a round and it popped open before I pulled it into place. After the first few rounds I wanted to open it back up to oil some more (for break-in) and it was stuck, couldn't get enough pressure out of my thumbs, so I tapped it down with a dowel against it, and used a piece of wood as a hammer. It unstuck after a couple of light taps. I inspected it and the receiver holes it slides into (upper and lower receiver) and there is no marring or any kind of obvious sign that could cause it to stick. It makes a very tight fit into the lower receiver. It was also -16F at the range, not that it should matter.

I also have an XCR-L and the receiver lock on it easily operates, so I believe this probably shouldn't stick the way it does.

Any advice on what I could do to ease that parts operation? I oiled it but it didn't help any. I'm thinking of taking an arkansas stone to it but I don't know where to start. The top side of the release lock that slides into the lower receiver has a rectangular shaped portion that is higher (length of lug, and 3/32" wide or so, and 50 microns high?) than the round lug itself, but I didn't see a recess for it in the lower receiver.

Please help!