Hello everybody, I have this mossberg 500 that I picked up about a month or so ago. The gun was just about perfect when I got it. I cleaned and oiled it up then put about 100 rounds through it. After that I loaded it up, stuck it in my closet and forgot about it. Yesterday I went to get the gun out to shoot it and saw this. I have a problem with field mice getting in my house. I guess they decided that my shotgun would be a good place to make a nest on/pee all over. I cleaned some of the surface rust off the gun, but the problem I am having is that I can not get the gun open to unload it. There is a shell in the chamber and the mag is full. I tried to press the slide release button in to release the slide back, the button pushed up and got stuck there and the slide is still locked forward. I also tried to shoot the shell that is in the chamber, but when I pulled the trigger nothing happened, like the firing pin is rusted/seized up and can't move forward. I liberally sprayed the gun down with oil and waited 1 day thinking that it would free it up but it didn't work. Any ideas on what I should do? I mainly want to get the loaded shell out of the chamber. Any help would be greatly appreciated, Thank you!