First of all, hangfires are potentially dangerous. If a round doesn't go off, wait a full minute before opening the bolt. There was such an incident at the 1995 1000 yard IBS Nationals. A guy (who had been experiencing hangfires all summer) opened his bolt after the rifle didn't fire, and it went off just as the locking lugs cleared. The bolt took off several fingers & went through his shoulder.
Hangfires *usually* (no warrenty implied here) are the result of primer-powder-case capacity issues. I'd second Steve, try a different primer. If you are using magnum primers, try a different brand. If you aren't using magnum primers, try some. If hangfires persist, try a different powder.
I have to add, this is a benchrest forum, and most of us are going to expect participants to have pretty extensive experience, and assume you are using a custom (i.e., strong & well-fitted) action. That said, and not as a recommendation, just a report, I've shot a .30 on a .404 case shortened to 2.5 inches, which has a capacity between a .300 Win Mag and a .300 Weatherby. I'd push 220 SMKs a bit faster than 2,900 fps (Oehler at 15 yards), using Federal 210 primers (pretty mild primer) and Reloader 22. As I remember, the RUM is the same body size as a .404 Jeffrey, and significantly longer than 2.5 inches.
Signs of pressure can be read off the primer, but ONLY if certain other things are known. Most important is, (1) is the case sized so there is only about .001 to .002 headspace? If so, you can get an indication of pressure off the flattening of the primer. Cratering of the primer tells you more about the fit of the firing pin in it's hole than about pressure. (2) Case head expansion. If you have micrometers, measure the case head, down where the brass is solid. If it's enlarging more than a certain amount, you have too much pressure. I'm not going to give a number, get it out of a book which has supposedly been researched & proofread. This is serious stuff & care is needed.
Good luck to you.
