Not a RUM, but ran a 300WM with a 24" barrel, speed was still reasonable, 3080fps with 180's and 2900fps with 200's.
Problem was it was LOUD. Muzzle blast was measured in feet not inches.
Now, all the magnums I run are barreled with 26" minimum.
They are less obnoxious at this length, sure, they may clunk a few low hung branches when hunting, but I tape my muzzles anyway.
I feel a 26" is minimum, but a 24" WILL still work.
Cheers.