I'm a little mystified with Brownells listing a 30 cal bbl for the 300 Win Mag with 1/2-28 threads...?? Is it a misprint, or does Howa really thread a 30 cal bbl for a 22 cal suppressor?
I've used Bell & Carlson stocks for several Howa bbl'd actions that came with the heavy/varmint contour bbls, but not in that specific stock. Stocks I've used with the heavy bbls are: 2093,1013, 6550, 6560, & 2998. If the bbl doesn't center in the stock's bbl channel after you've snugged the action screws, take a close look at the rear tang & how it fits into the inletting. If it's bearing on one side more than the other, that will usually be the cause of the bbl not being centered. Cutting a bit of relief in the side that's bearing on the tang will center things up; you just need to wrap enough tape around the bbl at about the mid point in the bbl channel before bedding so that it will center the bbl when the bbl'd action is put into the stock, and use enough bedding compound to fill the gap you cut at the tang area.