Both of them have had the problem since new. I usually use Federal American Eagle bulk box and I'm finding about 2-3% fail to ignite. I tried some 5.56 the other day and about 60% of them wouldn't ignite (worked fine in Tavors though)
I never really use 5.56, just happened to find a couple hundred rounds and thought I would use them up. So I'm not that concerned with 5.56 failures, it's understandable that their primers are going to be hard. But you would think that Federal .223 would ignite close to 100%
Round count is 2000+ each. I would think that it was because of wear but it's been the same since day one. I would also think that the firing pin channel was gummed up but they are clean and whenever I have disassembled the bolt they look pretty clean.
If I'm the only one with this sort of problem then maybe mine were installed with schitty springs.