I've done quite a bit of case reforming but haven't done that. But, it sure shouldn't be difficult, as case forming goes. Push the long 7mm into the short .350 die without the decap/expander rod in place. Trim the neck to near final length with a cut-off tool of some sort. Run the expander in it, then anneal the neck and turn it to proper thickness. Trim to final length on a case trimmer. Chamfer, deburr, you're done.
Yeah, sounds good. All except that first "trim" cut, right? Several options for that.
Best is to use a standard case trimming die, a fine tooth hacksaw, and mill file to finish. Can be hard to find the dies tho. I'm lucky enough to own my own metal lathe now so I make my own trim dies, I just cut a standard sizer die to the right length (carbide cutter bits are needed for doing that).
Before the lathe came into my life, I cut excess neck length with a high speed grinder with a 1/16th inch thick cut-off wheel, held in a vise. Just hand hold the cases to feed them in. It works but you need a grinder and fairly large machinist's vise to do it.
Before the grinder and big vise came into my life, I cut excess neck length with a hand held Dremel tool and small cut-off wheels. With care it can be done, and done safely too.
It's a shame the .350RM has faded so badly, it is a GOOD round. Much better than many seem to understand. Ditto the old .35 Whelen. But,....there's no magazine or TV glamor to them so the sales have stumbled to nearly nothing. The only thing getting publicity and market share today is the ultra-long range craze. And that's very unrealistic even if it looks/sounds really "cool." Oh, well....?
Good luck!
