For the price of a bolt, I'd just buy a new or used Tikka in a magnum caliber. Or try to trade with someone on here if your issue is swapping a standard to a magnum for a build.
Get your gunsmith to open up the bolt face on a lathe. that's what I did with my Tikka, originally it was a 9.3x62 had the barrel replaced with a 300WMag and bolt face opened up. happy as.