I guess eventually gun trouble will show up and if it took better than forty years to have gun trouble in the field I'm probably ahead of the game. Today the gun I was shooting decided it was going to start doubling. I had shot a few shells prior to it happening. After it happened the first time I only loaded the right barrel. After shooting that shell I again loaded both barrels and again it doubled. After that I only loaded the right barrel and hunted with the gun as a single shot. I have used this gun a handful of times but I had not shot it in 2-3 years prior to today. Never has there been any issues. It is a 20 gauge Zabala made in 1960. Prior to today I had only shot it with 3/4 ounce loads but I had a couple of boxes of 7/8 ounce loads that have been loaded for probably ten years that I was wanting to use up so that is what I was shooting today. I also noticed difficulty closing the gun after loading it about half the time. Either switching the shells to the other barrel or swapping out one of the shells with another one would allow the gun to close. Is there any chance that the problem is related to the shells and not the gun? I wish I would have pulled the back trigger after firing the right barrel to see if the left barrel tripped but I didn't think to do that. I just tested it here at the house with snap caps and it seems to be working fine. Any thought would be appreciated.