Re: Rifle Bedding
I got a .338 RUM in the 700 LSS, and had a similar pattern. VERY poor! Here's what I'd do:
1. Before spending any money with a 'smith, I'd call Remington and complain LOUDLY. They may have you send it back to them to be re-worked. I talked to a guy that had a .300 RUM acting the same way after +200 rounds and they hand-lapped the barrel and now it shoots sub-moa.
2. Skim coat the bedding on the stock. Easy to do and cheap.
3. Have the crown checked on the barrel, mine was ROUGH, you could see where the reamer chattered on the barrel when cutting the crown.
4. Work up some loads on it. Mine will shoot anywhere between a 9/16" pattern and a 2.5" pattern, depending on the load. Mine likes 250 grain Sierra Gamekings the best so far. Can't get better than 1" with 225 grain Accubonds, 1.25" with Hornady, and 1.5" with Speer.
5. Does the barrel foul heavily? Even after 250 rounds my barrel was still fouling badly. Had it checked with a borescope after THOROUGHLY cleaning it, and the barrel was still very rough. At the 'smith's suggestion I had to fire-lap it. Ggenerally don't recomment it, but it was either that or turn the barrel into a pry-bar.
6. Check your scope to make sure the scope or the mounts are not the problem.
7. Check yourself to see if you're not flinching badly and causing the problem. I put a brake on mine right off the bat, as the recoil is 2X that of a 7mm Mag. I had a Vais installed, and I'm glad I did. My shoulder is happy as well!
Good luck with your project. a 3" pattern really smells bad. The Sendero's have a good reputation for accuracy, so Remington SHOULD stand behind their product and fix it.
Mark in Utah