I am in the mist of doing a wood stock project myself, although i I haven't gotten that far yet. So far what i found out is...
1. there is a stripper called CitriStrip that is generally considered the least harsh and safest but is also considered the weakest. Meaning plan on multiple applications. Apparently this stuff is least likely to damage the original wood and also smells nice.
2. the only absolute safest ways not to jeopardize the wood is hand sanding. then again there the risk of over sanding, but my buddy with wood working experience (just not gun stocks) says not to worry about over sanding because you would really have to NOT be paying attention to go that far. when in doubt just use a finer grit.
I am tentatively planning on a combo method, one application of CitriStrip and then sand the remaining.