I've been looking at a drilling by Ludwig Borovnik recently with a full length tube insert, which would be surrounded by air, with 3 set screw adjustments about 1/3 of the way from the business end. So I've pondered this problem for a bit and really haven't applied pencil or physics to it but it seens that the glass is the problem. Basically the rib and the other tube is a heat sink for the lower rifled tube and possibly the whole lot moves. So if you only use iron sights at an appropriate distance would you see a similar variation or a closer point spread with the glass being the culprit? Or split your error with the 1st shot going an inch or two low and the follow up going an inch or two high with repect to the point of aim of the glass.
Kind Regards,
Raimey
rse
