Part I – Checking Rear Sight Assemblies
Folks, there is a good bit of “Ye Olde Art and Mysterie” about working on rear sights than many folks imagine and it is not an exact science nor a simple matter of replacing parts to get them right. What makes it even more difficult is that no commercial receiver is totally correct in the rear sight area. Even when you have a correctly milled rear sight area as on a REAL G.I. M14 or M1 Garand, there are still enough tolerance differences or tolerance stack up that can cause you problems. Also, there is no way a fix for one Rear Sight (RS) will automatically fix a problem with a RS on a different receiver.
The first thing I do when inspecting a real M14, M1 Garand or any commercial M14 rifle is to grab my pair of Brownell’s Magazine Tube/Cap Pliers. These have hard rubber like pads that will hold the pinion drum securely without damaging it. You could also wrap thin leather around the pinion drum and grab them with slip joint pliers. Then I use a screwdriver with a tip that matches the slot in the nut in the center of the pinion and try to tighten it. Usually, I find these nuts somewhat to very loose and that’s bad as they need to be tight. Sometimes all you have to do to fix a problem rear sight is to tighten this nut. I’ve also been informed the Brownell’s pliers were actually some kind of automotive pliers, but I’m not sure as I’m not an auto mechanic. Anyway, here’s a link showing these pliers.
Once you know the nut in the pinion is tight, it is time to check the windage knob to see if you can turn the knob. If it is too tight or too loose, then the nut in the windage knob may not be tightened correctly. What I have found to be the “sweet spot” for most sights is that when you tighten this nut, the first time it JUMPS into position is most often the correct amount of tightness. I sometimes go one more half turn when the elevation pinion has a worn triangular projection or the spring tension in the pinion is worn. If that causes the windage knob to be too tight, then you need to back off the nut to the first setting. SPECIAL NOTE: I have used this extra click of tightness on windage knobs that make it a little difficult to turn the windage knob to save the person from having to buy a new pinion. If WHILE you push inwards on the nut in the elevation pinion and at the same time then can move the windage knob, that may save you from having to buy a new pinion for a while. It isn’t as convenient as just turning the windage knob, but it saves you rather big bucks on a new pinion.
The next thing I do is run the aperture up about 10 clicks to see the clicks are solid and consistent. Then I leave the aperture there. I use my thumb to press downwards and forwards on the aperture to see if the aperture will slip and slide downward. Now A CAUTION HERE: On even the most perfectly fitted and working RS assembly, if you use enough pressure, you CAN AND WILL force the aperture down. That is NOT a valid test. If the aperture slips with very little pressure, you can try tightening the windage knob one more half turn. If that doesn’t fix it, you may be able to fix the problem with a tighter fitting rear sight cover, but you may also need a new elevation pinion. If that extra half turn on the windage knob does fix it and if now you can not move the windage knob, again you may need either a different rear sight cover or a new elevation pinion. On NM RS apertures, I run the aperture up to 30 clicks and try it again as NM shooters will often use that much elevation.
The next check is to turn the windage knob 12 clicks to the right and back to zero than 12 clicks to the left and back to zero. (24 clicks each way with NM ½ minute windage knobs.) This ensures the RS base moves correctly and comes back correctly according to the hash marks on the receiver. If the windage knob is too hard to turn or skips or catches, then a different RS cover is often in order OR you have problems inside the receiver.
The next thing I check is to push in on the right and then the left side of the RS base. You want the RS base to either not move or spring back when you release tension. This was not considered absolutely necessary on a G.I. rifle, but it makes for a more consistent rear sight adjustments. If it does not pass this test, usually you need a different RS cover.
There are additional things we check on NM RS assemblies, though that can go to a full book length to explain and really is too involved for anyone but an Armorer or Gunsmith.