Do I load these to same level as 350-grain SPEERS?
( Used 102 grains or so before with them.) Western Bullets order for (2) boxes of 50 each cast lead shipped runs about what 50 Hornady 400-grainers did on the shelf when you could get them. Scored a pound of RL-22 at LGS. No XMR-5744 available anywhere but Midway et al do show some Norma products available, MRP included.

Okay, 90 grains it is. Thanks for all the help...

If they'll run at that speed....

I'd want to know how the bullet fits the throat, how hard they are and how well the lube works.

Data for the Rigbone is light, pressure wise, so the starting load of 22 isn't out of line.

Be sure you aren't getting grey leading at the muzzle after sustained fire and the bullets are jammed;

Bottom line, if you see no leading, no lead star on the crown and you get sustained accuracy as the gun warms up, you're GTG.

Run an LBT 375 GC from my Rigby often; its a great cast cartridge...