rear sight loose on 1903

[Parashooter]

It isn't easy to tighten up a worn or sloppy '03 rear sight but it can be done if you have a light touch and go slowly.

Let's start with a picture of the components:



The repeatability of the windage adjustment depends on a good fit of the stud (a) in the hole (A), a good sliding fit between the rear lip (b) and the rear radius (B), full engagement of the windage worm threads (c) with the windage gear sector (C), and the tension of the worm spring (d).

The objective in tuning the sight is to eliminate play and binding. First step is to tighten up the stud/hole fit. If you have a machine shop you can fit a bushing after opening up the hole with an end mill, perfectly indexed. If not, peening the top of the stud until it binds, then lapping with fine compound (600 grit) will work for a while. Any play here is multiplied nearly four times at the leaf end of the movable base and, like a bad wheel bearing, no amount of tweaking the other parts will fix it.

Once the stud is a good fit in the hole, put the sight together without the worm screw assembly and tighten up the lip-radius fit (b-B) by tapping the lip in toward the radius with a soft brass or copper hammer at x-x. Test for binding by swiveling the movable base from side to side between taps. When it starts to bind, apply some compound and lap it smooth. Repeat the tapping and lapping until there is full contact throughout the normal range of movement, no slop and no binding. If needed, do the same for the front lip (e) which, when properly fitted, acts as a spring to exert a gentle down-pressure on the movable base and prevent it from rocking.

Clean off the abrasive, stone any burrs on the opposing conical surfaces of the worm assembly and its seat, make sure the worm spring (d) is not weak or collapsed (if it is, get a new worm assembly - they're cheap). Lube everything that makes contact with moly or graphite grease. Assemble the sight and center it.

Try to wiggle the movable assembly left and right with very little force to observe any slop. The last few thousandths of side play are sometimes impossible to remove without a new worm. Don't worry about them. If there is more than that, try peening the stud again.

Now push the movable base hard to the right against the tension of the worm spring. It should return itself to the original position without binding. If not, take it apart and lap some more. Be sure to clean out all the lapping compound.

Any tapping and peening has to be done very gently with a light, smooth hammer. The steel of the sight components is soft and deforms easily. Most components except the fixed base are widely available. If your '03 is in completely original condition, don't peen the stud - use the bushing in the hole on a spare movable assembly and keep the original assembly safe and unaltered.