I had or possibly still have the same problem and the only thing I can think of at this time is that when I ran the nylon brush back and forth through the bore and it swept the loose bore crap into the neck/chamber area on the brush retrieve and I didn't get it mopped out all that well. Since my scrubbing the rifle bore/chamber down with 50/50 kroil/bore cleaner solution, I've been pushing the nylon brush through and then unscrewing it and retracting the cleaning rod and it seems to be working on keeping the problem from resurfacing. I was thinking the loads were too low pressured that the neck wasn't expanding and sealing but with the powder charges loaded beyond max listings and the black on the necks still remained, that sort of ruled that idea out ...... Hopefully someone has the answer.
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