I had a 12 GA., Remington 11-87 with a cantilever barrel. My gun started failing to cycle the second shot (using Lightfield slugs). Instead of fixing it, I gave it to my middle son, who switched the barrel to his Remington 11-87, thinking the gun was the problem. Today he fired it and it was again a single shot, failing to recycle the second shell. I'm wondering if the pressure holes in the barrel are blocked. Is that a possible cause? Suggestions?