I've got a pair of UI 20's that I picked up at a pawn shop about 10 years ago. One of the things I've noticed is one will drop freely from all of my lowers when empty, while the other does not. After taking a caliper a measuring the widths of the magazines it looks like both are right around 0.885" wide at the base. One is 0.885" wide near the feed lips and the other is 5 thou wider at 0.89" at the feed lips. I've pretty much narrowed this down to the reason why the mag is hanging in the well. Any suggestions on potential fixes that won't trash the mag? I can live with it as those two 20's are the only straight 20's I have thus I typically use them only for hunting loads just thought I'd check and see if anyone had ever tried to get these back into spec short using a press (which I think may pop the top plug weld if not careful).

Just buy another metal 20. You have a stacking tolerance issue with the mag and magwell.

This is what you seek.

I wouldn't dick with it. Especially with range/hunting mags.

GunMagWarehouse has Okay Industries Surefeed 20-round gray magazines, 10 for $119.90

https://gunmagwarehouse.com/okay-surefeed-ar-15-223-rem-5-56-20-round-magazine-10-pack.html?queryID=c8ee292e4625ad16827b60d683f8fc52&objectID=10576&indexName=magento_default_products

I just bought some Okay Industries 20 round magazines from them. They look well made. My have the grey dry film on them. They are new, of course, but scuffed up. I'm fine with that. That's just the nature of that finish. If I had an old magazine like yours, I'd leave it alone. It is what it is.

Well, I had forgotten that I had another stash of magazines up in Colorado...which included some more UI 20's. I just did the logical thing and replaced the 20 that hangs in the mag well.