I have the .338 RUM in 700 LSS. Nice rifle, sub-MOA after some work on it. Put a Vais brake on it to save my shoulder. Have about 350 rounds down the tube this year.
I wish I had a Sendero, as they're more accurate - often sub-MOA out of the box with factory ammo, and the weight would help with the recoil.
My rifle likes the 250 grain Gamekings. 3/4" patter at 2950 fps. Could get up to 3077 fps but the accuracy dropped off. Lighter bullets such as the 225 grain Hornady or Accubonds, or the 200 grain speers are not as accurate. Haven't tried MK's yet, next on my list.
I shot one for a long while, great setup. Mine was custom on a 700 action but your's should be similar. I used the 300 Sierra and killed a pile of critters with it. (2 moose, several big whitetail, some wild hogs...can't remember what else). Mine kicked pretty good with the 300's... made snot fly out of my nose on ocassion
My standard load got about 2750 FPS if I recall correctly... could go faster but no need. There are many posts on this board with loads and info.
I have the 338 Rem. Ultra Mag in model 700 BDL I shoot nice 3 shot 1" groups at 150yds with all bullets made for it.I hand load For the 338 ultra and every gun I own. At 200 yds The 1" group turns into 2.5 group. But thats still not bad.
I've been shooting the 338 Ultra since Remington released it.It is a great round.I've shot most of my deer with that cartridge and never had one get away!The knockdown power is tremendous and it carries it along way!!I've started with the 700 Stainless Laminated.It was a great rifle.I just sold it Christmas Eve.Moving up to the Sendero.I put a Vias bake on mine and was impressed with how much it reduced the recoil.The load I worked up for mine shot under 1/2 inch groups at 100yds and still under an inch at 200yds.I only hope I have the same results with the new rifle.The load consisted of 250 Sierra Gameking over 101grs.of HODGDON RETUMBO and a Federal 215 match primer.Mine seemed to like the hevier bullets.Didn't have much luck with the lighter ones.Picked up a box of 210grn Scirrocos.Maybe I'll have some luck.You can't go wrong with this caliber for some long range hunting.I shot most of my deer beyond 300yds and they were dead before they hit the ground.Well I hope I've been some help to you.I really think you'll be impressed with this caliber.Good luck!!