The bronze tinted film looks like shellac. They really slopped it on at the arsenal. Try denatured alcohol to get it off of the trapdoor. Don't get any on the stock. It will strip the shellac.
Thanks hifi, but I'm pretty sure it's not shellac. Shellac would have stripped easily away with the brake cleaner, acetone, & CLP bath I gave it.
No, I believe it was/is some residual leftover from a lubricant or something that maybe had a copper or bronze component in it. Or maybe really old cosmo layer like that that turns Russian bayonets that kinda bronze yellow color. Slow, steady work with the 0000 steel wool, a toothbrush, and CLP did the trick. It just took a long time.
HR