pitting
A pitted or corroded chamber has been my experience too w/ the 742 family. The Remington autoloader will not tolerate any sort of neglect to the chamber concerning moisture or failing to be cleaned allowing carbon to reside and collect moisture over a period of time. I've fooled with 2-3 of them for acquaintances over the years that had the same issue described in the OP.
You get one wet, or shoot one, period, ...... wet or dry, .....you gotta clean it. The Remington auto rifle is a blue collar deer gun here, guys who cannot afford a BAR, buy the Remington, they are very common. The fast second shots available from the auto was a desirable thing back when hound hunting was popular........not so much now. But those who do not pay attention to their bore and chamber pay the price. Carefully maintained, they are serviceable autos,........but one cannot miss a beat caring for one.
Polishing the chamber is an option, and nickel cases as suggested helps some. So too, if you lightly lube brass cases, ie a wipe down, NOT dousing them, but that is only a superficial fix.