I had a 7mmRUM built this spring, primarily for 1K matches & the occasional coyote. I've posted on it here before, but here's a synopsis:
I tried 8 different powders & 3 different VLD bullets (used some Sierra 130MKs for a warm-up too at 3,671fps).
The bullets it liked best were Cauterucio (GTB) 176gr VLDs seated .005 into the lands. Also tried were Caut. 156s & JLK 180s. The 156s shot very well, the 180 JLKs not as well.
Powders tried were: IMR7828, RE19 & 22, MRP-2, H1000, WC860, H50BMG, &5010 pulldown. Luckily, the 5010 pulldown (milsurp) produced the best loads by far, & at $4.00 per pound was affordable to shoot.
The combination resulted in a .740BC bullet traveling @ 3,360fps. It consistently shoots sub-1/2MOA @ 300 yards & @ 3.25" 5-shot groups at 500. Wind is not much of a factor at 500.
It takes roughly 17-18MOA from a 100 yard zero to 1,000. Flat, flatter, flattest (maybe?). The computer shows it running @ 2,200-2,300fps at 1,000 but I have yet to confirm that. One of the other members here, 'Fatboy', has seen its trajectory personally through his spotting scope to 1,000 & can attest to its arc. It uses roughly 1/5 the windage of a .308 at 1K.
Throat erosion is measurable, but NOT extreme so far. Recoil is moderate, it has NO muzzle brake
, & I shoot it from a sling in conventional 1K LR matches, what it was designed for. I squeaked into the top 20 in the Wimbledon Cup with it this year at Camp Perry.
I have alot of tweaking to do with the load, it's still below its potential IMHO. I have some Retumbo on back-order, it's hard to get some powders down here in 'Mayberry'.
I was going to try the LRBT 162s as mentioned in another post, but with the performance I'm getting for the $$$ with Cauterucio's, I think I'll pass for .048BC - for now.
The 7mmMag is proven, the 7mmSTW is far more efficient in terms of powder burn vs. velocity, & the one conversation I had with Lazzeroni convinced me to never call back.
Hope this helps you. Good luck & good shooting!