Gee. I just happen to have one of those.
I haven't had to mess with the bedding at all, so far. 1/2-MOA for three shots, with most any old ammo. I did put a Timney trigger in it.
Anyhow, I've always shimmed out at the forearm tip after I've free-floated the forearm. I use kitchen wax paper, since it won't absorb moisture. I cut a 1/2" or 3/4" strip. Fold it back and forth for thickness until it takes about a five-pound pull to allow insertion of the shim.
If the groups stil aren't down tight, do like Scorch says and glass-bed. And work up a couple of tailored loads for it...
, Art