I've got an MVP V&P 24" barrel chambered for 5.56. I've put about a thousand rounds thru it, a mixture of .223 and 5.56 with no complaints. The ammo was a mix of PMC and bulk American Eagle, all 55 gr FMJ. Then I got into my case of Winchester 5.56 55 gr FMJ. All of a sudden I started experiencing a lot of duds, maybe as much as 15% of the rounds wouldn't fire. I did try recycling them and none shot. I disassembled and cleaned the bolt. While I was at it I measured the firing pin extension at about 0.045 inch. Then went to the range to see how that worked. It didn't. I shot a box of the 5.56 and got 3 duds. Recycling them didn't shoot them. For comparison I had picked up a box of American Eagle .223 55 gr FMJ. Exactly 1 out of 10 fired. So I gave up. Mossberg told me there is a known problem with the thicker primers used in 5.56. Before I send the rifle to them I wanted to see if the community had any suggestions. But the number of .223 duds is really bothersome. I can't believe that the chamber has eroded to the point the rounds don't headspace properly. But could it? The photograph shows closeups of the two brand duds, the bottom the 5.56 and the upper the AE. The dimpling is noticeably deeper in the 5.56. Thanks for the help.