Try putting the problem shell extractor rims into the rim recesses at the breeches backwards and turning and rocking them to see if they're tight in the recesses. I have had three guns that had/have tight recesses - a repro28, a vintage Dougal 12ga, and a DH12. None of them like AA hulls and will stick closed solid sometimes. The DH12 I could always break open over my knee...not good... the repro28 would require being put into a rubber-jawed vise to close it even tighter so the lever could be released.... VERY scary that one. I bought a Clymer rim recess reamer and reamed the Dougal out a tad and the reamer is now on loan to a friend in Anchorage who has tight recesses in a nice old LC. I did not ream the DH12 because when I put the spring-loaded piloted reamer into the chamber the cutter did not hit evenly on the breech faces, which apparently are not orthogonal to the bore/chamber centerline for whatever reason. Reaming them out would have made part of the recess too deep and I wasn't going to go there - I just shoot STS in that one exclusively. They all digest STS hulls or any old paper shell with no issues at all. Some modern shotshells are are not made with much precision, especially AA's. Try taking a micrometer to the rims of various brands and you'll see how out of round some are - again, especially AA's. Mic the old paper shells and you'll find they are nice and round and made of much heavier metal that stays that way. This is not a new or unknown issue. I think Bill Murphy has a home made 28 ga rim recess reamer that has made the rounds to folks needing it. Mine is also available for loan for postage costs only if someone requires it. It cost I think $115 originally from Clymer in Michigan and is a beautiful piece of work.

Shot the GH Parker and th Lefever G 16 yesterday and had the same problem closing the gun only with the RST's , no problems with the RGL's or Win. shells. The rims are visibly thicker on the RST shells and that seems to be the problem. I will take a few to my machinist neighbor and let him measure the thicknes with his micrometer. I was going to order a couple hundred 2 1/2" cheddites to load , but not now. I will just continue shooting the other shells.

just a thought, I am going to make sure that on the initial resizing on my Mec 600 yhat the arm is fully depressed. Does the resizing affect the rim thickness? Since the old primer pops out before the resizing is complete, perhaps I am not fully depressing the lever at times. Back to the reloading bench!!