#4 Mark 1 Loading problem

[Prairie Fire]

Last night I fixed a mag that had been giving me fits for some time. It had the same problem as the mag of the original poster: that of failing to strip a round.

The correct diagnosis, came from looking at the gun from a different angle. I set the gun on its butt, vertical, and while pushing the bolt home, straight up, I noticed that the bolt face would pass over the left-hand round. If the bolt was tilted down a bit while being closed, the bolt face would catch the round (so much for the failure percentages, as the original poster talked of. Slow feed may mean a straight closure with no round picked up, while faster manipulation may lead to running the bolt "downhill" and picking up the round.)

This bad mag was compared closely with a good mag, both loaded and unloaded. Feed lips, spring length, etc., all looked real similar. With the unloaded mag in the rifle, it finally became apparent that the left rear feed lip was making contact with the corresponding rounded surface inside the receiver ( body.) I took off a few thousands from this mag lip, radiused the cut, and retried it. That small amount of work got the mag to seat noticeably higher in the receiver, and got it to present the round in such a way that the bolt head cannot miss picking it up.

That may or may not be the OP's problem. Just thought I'd throw out another possible fix not mentioned yet.