Tanzian, good point for alot of calibers, but won't work worth a darn on a 300RUM, or Weatherby cartridge. You could never reach the rifling and still fit in magazine. SAAMI says 3.6" max, but you would have to load way out past 3.85" or so to hit the rifling on a 300RUM reamed with a factory spec'd reamer. And if you get a custom throat, like some I know, where you could touch the rifling at 3.62" or so, you can throw away your data manuals on the 300RUM. They will be way off.