Drum magazine stuck in gun

[TaroBear]

I've got sort of an amusing problem. I've been having some feed issues with my PPSh drums. Some friends told me it might be that I've kept the springs down with BBs too long, so I decided to empty all the mags and let the springs settle for a good month or so. Yesterday, when I decided to test the mags, I tried to take one of the drums out of the gun (it's kept on a rack with an empty drum in it), and I just couldn't do it. The drum is stuck in the gun. I tried applying various different types of pressure to the release, and it won't budge. I've tried every conceivable motion to gently take the mag out. I even broke the gun down to see if it was aligned properly. It looks like it's in there correctly, with the lips lined up. No amount of tugging has worked. My next experiment will be to try and drip some lube down into the sides to see if it'll loosen it up.

Any ideas what's wrong?