[ithacaartist]

Here's something to try: I'd check the overall assembly, holdopen and safety first, as described above. It may be possible to move the upper backward by the influence of a padded bar clamp setup. Locate one end of the clamp at the muzzle, the other at the rear of the frame, and gently squeeze until the locking bolt will rotate. Don't use a lot of force, try to "feel" what's going on as you go. It may also help to warm the gun up a little bit in the toaster oven, maybe 200 degrees, which I do not think will affect springs and other heat treated parts.
If the front of the frame has been pinching the upper, you may see evidence of it after field stripping.