Is that one of the "Gauges" which is a case with a drilled out primer pocket and over sized neck so that you can manually push the bullet to the point where it contacts the rifling then lock it down? If so, then that's where you'd have to seat to touch the rifling. That doesn't mean that will give the best accuracy though. It's a good reference point and something to try with good odds that accuracy could improve. In my opinion "distance to rifling" get's overplayed now as far as making a blanket statement that a given brand and weight of bullet ALWAYS prefers this or that. Every rifle is an individual. You are certainly getting consistent velocities already. I'd use that OAL you just got from the picture above as a MAX and start seating out from where you are(have been loading) .010 or .020 at a time and see what happens. Also check to make sure your magazine can handle whatever OAL you end up going with. Although I have hunted with an OAL beyond the magazines capability before and reduced the rifle to one shot in the chamber with one on the follower. Rarely will you ever be able to fire more than 2 anyhow.
