Welcome to the wonderful world of the Ultramags! My .300 ultra on a 700BDL did the same thing, until I added a Vais muzzle Brake to the end of the barrel
Hold the butt of the gun firmly against your shoulder. It'll prevent the rifle from moving far in relation to your body when shooting (kind of). Recoil on these cannons is respectable. More like artillery!
Get a Vais brake and life will be better for you, but MUCH worse for everyone else at the gun range. Use ear plugs AND muffs.
im trying real hard to not get a break.if i can't get it to shoot like i want it to im sending it to rw hart for a new barrel.i don't think i will have to its doing good.i just called sinclair they are sending me a jewell trigger set at one pound.the factory trigger is almost 6 pounds.im getting groups of a inch and less.4 shots will be .5 and one sucker has to screw it up by going an inch.between the new trigger and im going to get some new glasses it should be ok as it is.my eyes are not as good as i would like them to be.