My Mac 90 has always cycled flawlessly regardless of what I've fed it. I would try the brass 20ga bore brush method commonly used in the Mosin chamber. Make sure the gas tube is clean and unobstructed and everything else is clean and lubed. You can over lube, be conservative. These things are made to function under extreme adverse conditions so it should be easy to trouble shoot the problem.
"War is an ugly thing, but not the ugliest of things. The decayed and degraded state of moral and patriotic feeling, which thinks nothing is worth war, is worse. A man who has nothing which he cares more about than his own personal safety is a miserable creature, and has no chance of being free unless he is made free and kept so by the exertions of better men than himself" John Stuart Mill
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