I have a 7mm Ultra that is set up as a target rifle. Recoil is very comfortable & the ballistics are superb. It is very likely going to be a world class throat eroder.
I'm getting 3,300-3,400 fps out of a 30" Kreiger 1:9" barrel with 180gr JLKs. 130 Sierras went out at 3,671. It is much less 'efficient' than the STW for the amount of powder it uses. I only have @ 150 rounds through it trying to find a load/powder it likes.
Some interesting finds so far:
* It only requires @17 MOA from 100-1,000 in elevation.
* It takes @ 1/4 the wind drift as a 308 at 1,000.
* The time of flight at 1,000 is almost exactly 1/2 that of a 308. :razz:
* Where a 308 will just tip over a 12" T1 steel plate at 1,000, the 7mm RUM will flatten it & make do backflips.
It's too soon to tell much else.
All 'standard' powders I've tried so far leave 1/4 - 5/16" of the case unfilled below the shoulder. I'm messing with BMG powders (H50BMG, WC860, & 5010) lately & am seeing some improvements. The longtime longranger is right: a l-o-n-g barrel is advised due to the serious overbore.
The good part is, a 180gr VLD or similar should give downrange (not necessarily terminal) performance out to 1,000 approaching a big 338 WITHOUT the recoil a whopper 338 projectile will give ya! It also has impressive sectional density to help it on target. The ballistics programs I've run the numbers on show that the 180 should still be doing @ 2,200 at 1,000 & @ 1,500 @ one mile. It is a shame the throats probably won't last.
I do want to try some of Warren's 162 LRBTs. I shot a group in a tricky fishtailing wind last week at 500 yards that could be covered with a fist. Not bad for a preliminary load. That was with a 156gr Cauterucio.
I wish I had more to offer, but I hope this helps you a little.