Been kicking this one around myself as I happen to have stumbled on some .30 Gibbs dies for a song, have a mountain of ‘06 brass and .30 cal bullets of almost every flavor, a potential donor .30-06, and a good gunsmith that will punch it out for a reasonable fee.
No doubt gains are modest but most real world reports show 100-150 FPS gains (some of which could very well just be from hiding pressure signs).
I kinda view it as a long action .300 WSM with cheap brass and 4 in the magazine.
