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Are your magazines Remington made magazine or are they aftermarket magazines made by someone else?
It almost sounds like the spring holding up the hold open device is the problem, or, the hold open device is binding and sticking, not allowing it to disengage.
When the last round is fired, the magazine follower pushes up against the hold open device part which holds the bolt open. Pulling the bolt back slightly if a new magazine has been loaded or with no magazine in the rifle, should allow the spring pressure of the hold open device parts to push the hold open device downwards out of the way of the bolt, allowing the bolt to go forward.
If the bolt is forward, and a loaded magazine is inserted, then the follower is not in contact with the hold open device, and the bolt when pulled back and released will chamber a round, until the last round when the magazine follower engages to hold the bolt open.
Therefore, I would suggest you look at the hold open device spring being too weak, or the parts in the hold open device binding slightly when using a 30 round magazine.
Again, answer the question as to what brand of magazines are you using --Remington large capacity or aftermarket manufacturer. There has been problems with aftermarket magazines. Does this happen with the factory 10 round magazines too?
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