I was just given a single shot bolt action .22 that is marked "marathon products" and says "made in spain". The guy I got the gun from has had it in his closet for 20 years so it is fairly old. Does anybody have an idea of what model it is and when it was produced? There was a little rust on the outside of the barrel and bolt, but the chamber looked good and the rifling in the barrel looked fine as well. I took it out to shoot it this morning and fired a a couple shots. It fired , but on the first shot I noticed that the sound of the shot was low and muffled. I figured it was just a bad round, so I chambered another round and being extra careful, I fired another shot. This time, it sounded normal, but somehow it spit burning powder back at me. I dont know how it happened, being a bolt action, but it did. and obviously I wont be shooting it until I can have someone look at it. What could have happened?