What is a good conservative amount of gap to have between barrel and stock? Thanks

Don’t go too big since you will end up with pine needles and everything else getting in there.

I use pillar bedded McMillan stocks and I can easily slide a 3x5 card between the barrel and stock from forend all the way to the recoil lug. Much less than that and it may touch when things heat up...much more and you run the risk of debris getting in there.

If one can pass a dollar bill between the barrel and stock it's fine to go IMO.

In otherwords......010 gap is all that's required