Yes, it will work on an M. No, you'll lose forward assist.I wrote to Mountainman directly with some questions about function and availability of his folding charging handles. He appears to be quite busy (who isn't?) and failed to answer a couple questions. I was hoping this forum could fill in the blanks for him.
Will this folding charging handle work on an XCR-M?
Was the forward assist addressed?
He said he will begin working on them "next month", which should be July or August of 2021, depending on how you look at it. Look forward to it.