I rebarreled a customers 300 RUM with a 26" #4 Rock Creek Sporter, 1:10, 5R, with a Harrel's Muzzle brake. The rounds are being loaded with 180 Nosler Balistic Tips or 180 Swift Scirocco II. The throat has been opened to 3.315" Thus giving the bullets a .200" jump. I shot 5 shot groups with Reloader 22, H-1000, Retumbo, H-4831SC, IMR 7828. The brass was Remington, Primers were Federal 215 GMM. I full length sized, trimmed, chamfered, anealed, and cleaned primer pockets, between reloadings. My loads with H-4831SC were sub .5moa. and the loads with Retumbo were sub 1. moa. I shot velocities between 3,150 and 3,300fps. Quite a round. I shot over 100 rounds today.
One thing I noticed with the H-4831SC was I shoot 78.5grains with 180 Scirocco in my 300 Win Mag to get 3,1150 fps. With the 300RUM I was shooting 86. grains to get basically the same velocity.
With the 300 RUM it will be nice to be able to shoot 150 grain bullets at 3,400- 3500 fps.
Hell, if I can get the 180's I use to 3300+ fps with rl25 in my rum you can take a 150 to 3600 fps. You are using rather fast powders in your 30 rum for full speed ahead though, especially for 180 grain + bullets. You should nearly be using 50bmg powders. I use rl50 with 225 hornady hpbt's and imr 5010 and wc872 also with both doing very well at modest pressures. It really sucks that my i 5010 went bad as I had a 180 doing 3320 with it at 5 grains below top load tried. I didn't chrono the run-up though so I can't tell you what max was. I need to get some 5010 again but it's very hard to fing good 5010 lately. WC 872 will get you to 3300 fps with a 180 at about full tilt, but I like rl25 better.
Just measured the 91.5 group center to center...... .48. I was thinkin when you measured a group size it was edge to edge. The 92 grain group center to center went just shy of .75 so I think we'll be able to find somethin right through there somewhere.. Lookin forward to shootin with ya Roy. Dan