Sighting in Old Rifles

This is a Russian Mosin-Nagant 91/30 sniper rifle. It was the standard Russian service rifle and in this example, it has a 3.5x PU telescopic sight installed. This particular type of rifle was probably made in more numbers than any other sniper rifle in history.


Like any rifle with new sights installed, they need to be aligned. The first step is to boresight the scope. This is done by setting the rifle into a steady fixture, then moving the fixture until a target is visible down the bore of the rifle. This is easy to do with a bolt-action rifle; you just remove the bolt and look through the bore from behind. You then align the scope with the same target that you can see through the bore. (You can also buy a laser gizmo that will project a beam that shows up on a blank surface and then align the scope with that, if you feel like paying the money to buy such a contraption.)

Nowadays, boresighting is mainly done to save ammunition in the final sighting-in process, for a boresighted rifle will shoot very close to the point of aim, and then the shooter can make the final adjustments on the scope. When you adjust the windage (left/right) and elevation (up/down) turrets on a modern scope (the two knobs seen on most sights), the crosshairs do not move, they remain centered. Rather, when you make an adjustment, the entire field-of-view of the scope moves.

Older scopes were not like that: When you make an adjustment on a scope sight of an old design, the crosshairs move. So what you do in order to boresight is you center the crosshairs (also known as the reticle) and then you make adjustments on the mount to move the entire scope.

This is the scope mount on a Mosin sniper rifle. If you look on the right side of the mount, just in front of the big knurled knob, you will see a small set screw. There is one like it on the bottom side. Those setscrews are used to sight the rifle in for elevation. Those screws are on the mounting plate that is fixed to the rifle. The scope and its mount are locked into place by the knurled knob.


Adjusting the scope in windage is trickier. If you detach the mount itself from the base, on the inside of the mount, behind the wedge where the knurled knob locks it in place, you will find two small "feet". In the photo below, they are the shiny horizontal lines. They are at the back of the mount; the mount has a socket machined into the front of it and it pivots on a matching ball protrusion that is on the baseplate.

All Mosin scope mounts come from the factory with oversized feet that will aim the scope well to the right of the line-of-sight of the rifle's bore. In order to boresight the scope in windage, you have to very carefully grind down the two feet. I say "carefully", because if you remove too much metal, you then have to shim the feet to bring the scope back in line.

Once you get it set correctly, you can go off to the range and make any final adjustments. Once the elevation is set, you should either stake or loctite the bottom elevation screw (not the top, in case you want to remove the scope and mount) and re-blue the feet to prevent rust from forming.

(For more detail, read this.)

Or you can buy a modern scope where you don't have to do any of this, but where is the fun in that?