I believe you could bust a sizing die on an RMC case. But you could probably also turn them down once or twice and have still plenty of brass left over.
I wouldn't put a RMC hull in a conventional sizing die. I use a block of steel that someone drilled a 10 gauge diameter hole in and either use the arbor press or a sledgehammer with sizing wax. Even so I have 8-10 that are still too over sized to fit in my 10 gauge and that won't fully re-size using my method.
I experimented w resizing 16 ga RMC. Oversized press and lubed dies were a failure. I even tried blow torching the brass to softened it with minor success but still more pain than gain. I have to try your steel block technique
Ultimately, my solution is to limit use to guns with near identical chamber size and keep lots for different guns segregated.
