I've heard 50 fps as a rule but there is simply too much variability between individual rifles to make such a broad statement. The 300 will always have an advantage over the 30-06 as far as velocity is concerned. It is simply put a matter of displacement. If one looks at a rifle as an engine with the case as the displacement, and all else is equal the larger the displacement the more energy is produced. If the bores and the bullet weights are the same, the energy will express as velocity. The trade off and biggest disadvantage of a short barreled 300 mag of any flavor is the increase in muzzle blast.. and this far ofsets any gain in portability one might gain from the shorter tube.
