I have rebedded both of my 257 Wthrby's and had the same issues with bedding/grouping. You NEED a pressure point with factory barrel/stock configuration. I learned this from my Lazermark, which I immediately applied to my Lghtwgt. I used the shim technique as you have at the range to attain the grouping with the particular handload I wanted to shoot. Then I bedded them. It now shoots pretty much .5 all day long any day with the first 2 round cutting, the 3rd a little outside 10;00, both of them. I do not know of the #age applied pressure to the barrels. I do not shoot anymore than 3 shot groups and you let the barrel cool completely between groupings. I dont time or care to time between shots as you don't do that in the field hunting.
The torque I use on the Lgwht. is 65"lb's, factory torque. I can't remember the torque on the wood stock I use. If you call Wthrby I'm sure they'll give you a torque number.
I shoot H-1000 in both my rifles for my hunting loads (115 grn bullets). I had used RL-22 with the 100grn bullets and still would if I used that bullet. This is what I know about Wthrby's. You might want to look at some loads for the 270 Wthrby at... Steves pages
Hang in there you'll get her shooting and if its a factory barrel both of mine shot better after 200 rounds for what it's worth.