1) Geek factor. It's way cool. Good topic around the firing line.
2) When going from standard belted magnum, to RUM or Lapua in same action messing with the rails to get it to feed is a pain (hate to pay a smith for stuff like that /ubbthreads/images/graemlins/crazy.gif /ubbthreads/images/graemlins/crazy.gif)
3)There may be, oh! let there please be, some action stiffing as a result of the installation.
4) Gives a much larger bedding surface.
5) Geek factor #2. I like the single shot idea. Always have.] /ubbthreads/images/graemlins/confused.gif
I'm about to be in a situation where the overall cartridge length is too long for the magazine. A 12 buck or so + installation isn't a bad solution.