Seems like I'm in the Mr Fix-it mode lately, after fixing the synthetic forend, I decided to tackle the off center issue on the BC Carbine forend I bought second hand recently that's on my 405 Win, I noticed a gap between the spacer and the frame on one side, none on the other even tho the forend fits snug, this forend and a couple other walnut forends all appear to have the mounting hole drilled off center which makes the barrel off center in the forend channel. So I eye-balled what it would take to center it, mounted the forend in leather in the vise on my mill, chucked up a 3/8" end mill(a drill press would work too I think) centered the end mill in the existing hole, then moved the table over about .050" and made a new hole off center what I figured was enough to center the barrel.
Then I used a ½" drill to make a new countersink for the mounting screw, drilled it just a tad deeper than the original hole so it would center on the new hole. Then I cut a section of 30-30 brass, cut it in half so I had a "C" shaped shim, tapered the ends so it fits in the forend hole to keep the forend in place, pushed it in place and installed the screw, worked perfectly, all that's need now is to epoxy the shim in place and Tru-Oil the wood. I think this would work to tighten up the fit on the synthetic forend too.
Tim