I finally got a chance to toss some 6 RPM rounds over the chrono tonight. Best powder tested so far was VV 24N41. 72 grains tossed the 115 Berger out at 3600+fps.
Krieger 1:7 twist, 26.5" long.

Here are a few other powders I tried.

68gr H50BMG 3250fps
71.5gr US869 3500fps
73gr VV 20N29 3350fps

So lets get the "Barrel Burner" comments out of the way now. No need for that. Barrel burner, chamber 3 barrels at a time, the barrel will be worn out before you develop a load, throat eater, horribly inefficient, what can that do that my 6mm Creedmoor can't, solution looking for a problem......and the Campfire knuckle dragging drivel will go on and on. If that is all you have to say, just move along.

Tony Rumore
Tromix

pic left to right, .243, 240 Weatherby, 243 Catbird, 6mm Weatherby RPM

Edited to add - no accuracy testing. I was firing it on the 50 foot Tromix indoor range.

[Linked Image from i.imgur.com]

Last edited by TonyRumore; 11/27/23.
Run it up, until you blow it up, then back it down a bit.