[ithacaartist]

If that original mag was worn enough to almost obliterate the serial numbers on the base, I'll bet the notch cut into its body is worn enough to cause the problem. When the mag is inserted, the mag catch ordinarily clicks into that notch and holds the mag within the mag well. The height at which it is held is determined by the upper edge of that notch and the upper lip of the catch. With sufficient wear on either/both, the breech block will miss picking up the next round entirely when returning to battery. The good results you had when holding the mag up manually when taking a shot are further evidence that this was happening.

For shooting, it's good practice to use a dependable mag other than a collectible original. This is particularly true when you have one of the earlier. wooden base mags because--as you've experienced-- the bottoms crack and vlow out. I wouldn't sweat it too much in your case since the mag sounds as if it was kind of on its last legs anyway. Even if the body is worn beyond repair and the bottom is but a memory at this point, its original guts have at least some value as spares. G.T., a member here, is the go-to magazine wizard, and has turned many sows' ears into silk purses in this realm, so you would do well to P.M. for his opinion about what might be done.

In the meantime, order yourself up a Mec-Gar mag or three to use for shooting, as they are currently the best available for reliable performance.

p.s. Don't forget those pics!