Bonus find at the range today.

[Sentryduty]

so Colt mags have a "pinning" issue by the look of it. Will post in the pictures in the AR forum in the next couple of days.

I have encountered this as well from time to time, and simply dress down the head of the rivet until it no longer interferes with seating of the magazine. If the rivet used is made of steel it can be polished smooth and darkened with a dab of cold blue for a nice finished look.

Sometimes importers get over zealous with magazine limiting to the point of hurting proper function, I have a number of excellent quality 15 round M1 carbine magazines that have been pinned too tight to allow the loaded magazine to seat on a closed bolt. I am still pondering how I am going to fix that without making a dog's breakfast of it.