I have an M2 in 20 gauge with a rifled slug barrel that is cycling inconsistently. When it "jams" the spent casing is stuck between the bolt and the front of the ejection port. If I pull the bolt back and release it, it ejects the spent shell and loads the new one.
Some ammo it happens more than others. Light fields hang up more often than not. Despite the name, they are not a "light load". They shoot a 7/8 oz slug at 1500fps. It's to bad because it shoots these very accurately. Brenneke 3 inch mags are better, but still hang up occasionally. I have tried many other slugs, and eventually they all hang up.
This has been happening since it was new. I have called several times and tried everything they recommend as well as anything I could think of. Cleaned it and used less oil. cleaned it and used almost no oil. Cleaned it and used dry lube. None of that made a difference. I replaced the recoil spring with one of the aftermarket ones that are supposed to help slam it shut, and that wouldn't cycle hardly at all.
They told me that sometimes there is a break in period and I need to fire one to two hundred rounds through it. This is one thing if your shooting skeet, but I only have a rifled slug barrel. still, by this point I must have over 100 rounds through it.
I'm getting frustrated.