DISCLAIMER: I make no claims of being a gun expert regardless of what it says below my board name. Anyone who follows my instructions does so at their own risk. The safe thing to do is to take it to a gunsmith.
Put safety on. Pull operating handle to lock bolt back. Remove the magazine cap, forend, and barrel. Also remove the piston and exhaust valve spring. Observe a small pin/rod that fits crossways near the front end of the magazine tube. Take a small punch or nail and press in on this pin while simultaneously turning the shaft that protrudes from the front of the magazine counterclockwise. Be careful after giving this shaft a couple of turns, because the magazine spring is compressed behind it. Wear safety glasses. Continue to unscrew the shaft until the shaft comes free from the magazine. Behind the shaft is the compressed spring which will try to escape. Be careful that it doesn't pop out and hit you in the face. Once you remove the spring, you can take a small rod and push the shell back toward the loading port in the bottom of the receiver. By holding in on the little shell stop on the inside of the receiver, you can remove the shell from the magazine out the loading gate. Be careful not to hit the bolt release button on the right side of the receiver. It could damage the gun, and it wouldn't do your fingers much good either if they get caught between the bolt and the front of the ejection port. :lol:
Now that you've got the gun apart, clean the inside of the magazine tube and oil it lightly. Put the magazine follower back in place. Insert the spring back into the magazine tube. Compress the spring and put the shaft/cap back on by screwing it clockwise until the pin locks into place in the little hole in the side of the magazine tube. Be careful again. Wear safety glasses. Once that's assembled, just reassemble the rest of it in the usual manner.
BTW, next time, don't stick those mis-shaped reloads in the magazine tube. :wink: :lol: