Help with a Remington Mohawk 48 12 Ga.

[Guest Rick M&P45]

A friend gave me a Remington Mohawk 48 12 Ga. self loading shotgun about 20 years ago and I just fired it yesterday for the first time (I know). It was used but look very clean. It went Boom but the barrel slid back about 2 inches and the round did not eject. I pulled the barrel back to its correct location and the emptied the shells. I brought it home with no futher tries at firing it. It does not have a barrel nut to hold it in place. It does have a ring on the bottom of the barrel that slides over the mag tube and slides next to a spring that fits between the "ring" and the body of the gun. Do you have any ideas on how to correct this problem?

[MasterBlaster]

A friend of mine's Browning sweet16 will do the same thing, and we cleaned and lubed the shell tube on the spring and it stays put, my old Sportsman 58 Remington trys to act up when hot and dry too sometimes?