I have done a few stippling projects and the hardest part is to get a straight clean border. The stippling is easy, the edges not so much.
it does not look like the existing butt stock has very straight lines either... I could see where that would be a challenge making straight lines with a round tool... I'm no gun smith but my immediate thought was to cut the border with a checkering tool first also...
Be interesting to see how it turns out and what method works best.