Elementary Front Sight Adjustment for the K31:
Remember to move the front sight in opposite direction that you want to move your shot group. If you need to move your group to the left, move the front sight to the right.
The front sight blade on the K31 is mounted in a dovetail that is on a bias of about 10 degrees with the axis of the bore. That makes it easy to make very precise adjustments, in comparison with most military rifles. The geometry looks like this:
The numbers are significant, as we shall see.
I use a small sight adjuster like this on the range:
In the picture, the adjuster is set to push the sight away from the muzzle, which also pushes it to the left, because of the angle of the dovetail. This would move the shot group to the right.
So how much will it move the group?
The sight radius of the K31 is about 22.5". It will vary a little bit depending on the fore/aft position of the front sight blade and the elevation setting of the rear sight, but the variance is not significant. Calculating how much movement of the sight will give a one minute-of-angle change is fairly straight-forward. Recall that a minute of angle is 1/60 of a degree, and doing some high school trig:
Plug in the 22.5" sight radius, and you find that .0065" of movement perpendicular to the bore will change the point of impact of the shot group by one minute-of-angle, or approximately one inch at 100 yards, on the K31. The illustration shows an elevation change on the rear sight, but that movement can be in either windage or elevation with either the front sight or the rear sight.
The pitch of the screw in my little sight adjuster is 1mm. That means one full turn of the screw will advance the adjuster one millimeter, or .039". If you look back at the geometry diagram of the front sight, that .039" of movement on my front sight adjuster will move the front sight .0068" perpendicular to the bore, and that's pretty darn close to the calculated value of .0065" for one minute-of-angle.
UPDATE:
I have an annodized commercial front sight adjuster that is marked for the K11:
This same style is available for the K31, the base is annodized blue and it is stamped K31. I only bought the K11 version since what I have for the K31 works
just fine. I suspect the difference between the K11 and K31 versions is the dimensions of the mortice in the base where it fits over the "ears" of
the front sight. These are slightly different on the K11, but the sight, and the adjuster, works in the same way. I also found the "K11" adjuster
works just fine for the K31 if you attach it with care.
The pitch of the adjusting screw is 1.25, so one complete turn of the screw moves the front sight blade (1/25.4) * 1.25 = .0492".
Do the trig, and it moves the sight blade .00867" perpendicular to the bore. That's equivalent to 1.33 MOA, or 4/3 MOA. A half turn would therefore
be equivalent to 2/3 MOA, and a quarter turn equal to 1/3 MOA.
HTH ...
Resp'y,
Bob S.
