Before going further, perhaps it is best to write about how to move rear and front sights right or left.
First one needs some kind of drift or punch against the side of either sight that is struck by a hammer to move the sight. It is EXTREMELY important to use a drift punch that is softer or at least no harder than the material of the sight, so you don’t ding up the sight with the drift punch. Sometimes one can use a hard wood dowel or Nylon Punch for this, but many times one needs something stronger than that and Brass or Bronze are normally the materials of choice.
There is no need to buy a set of Brass Gunsmith’s Drift Punches to move sights. If you know someone who works in a machine shop, perhaps they can get you a four or five inch length of ¼” Diameter Brass Rod. If not, go to a Boat/Marine store that carries supplies. I bought a 4” long, about ¼” diameter, round head domed Brass bolt (like a carriage bolt) years ago from such a store and it is my favorite punch for moving sights and other things. After filing off the machine threads, I filed the end to a rectangular shape and it is just the ticket to move sights. Then I filed a flat on the rounded dome and that is where I hit it with a brass or steel hammer.
Oh, another nice thing about using a brass or bronze drift punch is that you normally can’t see where it hit on a brass front sight. On an iron or steel rear sight, it leaves a little “wash” of brass color, but that can easily be cleaned off using one of the modern bore solvents designed to remove copper. Put some solvent on a Q Tip and rub hard on the brass “wash” and it will take it off without harming the finish on an Iron/Steel sight. Just make sure you oil it afterwards so it doesn’t rust.
When moving a Front Sight, it is EXTREMELY important you DO NOT hit the blade as you will bend, crack or even bust the blade off the dovetail base. Yep, I’ve seen folks do that too many times and that’s why I mention it. It is best to hold the gun in a padded vise, but at the range maybe you can get someone to hold the gun for you or lay the gun down on a pad on it’s side. You place the drift punch as close to the bottom of the dovetail sight base as you can and keep the face of the drift punch as even as you can with the dovetail. (You may need to file the drift punch so it is a smaller than the side of the dovetail or turn the punch so the smaller side of the rectangular shape is against the dovetail.)
Unless one is a Rifle Builder, most of us won’t know how tight the sights are in their dovetails when we go to adjust the sights. So when you carefully place the drift against one side of the front sight dovetail base, tap it lightly at first to see if it will move the front sight. If not, tap it a little harder. Keep trying to tap it a little harder each time until it just starts moving the sight base.
Something one may not think about is how can you tell how far you moved the sight? I normally use a 6” precision Machinist’s Rule (Steel Ruler) but most folks won’t have one of those. All you really need for the job is a Very Fine Tip Black Permanent marker. You draw one line on the sight base close to the middle and extend it onto the barrel. That way you can see how much you move the sight base each time and sometimes it will show you where to drive it back if you went too far or in the wrong direction. (Yep, that is bad experience talking. Grin.) When you are done moving the sight, some bore cleaner or Acetone will clean off the black mark and then oil it to ensure the barrel and sight (if Iron or Steel) doesn’t rust.
OK, so how far do you move a sight? There are mathematical formulae for different calibers that talk about moving the sight a fraction of an inch to move the strike of the bullet one inch at 100 yards, but to be honest, they are at best only a guide to moving sights. In the hundreds, if not thousands of front sights I’ve moved over the years, I found it wasn’t necessary or even much useful to use those formulae. There are too many differences in the way each shooter see’s the front sight. What I suggest is try moving a sight maybe 1/64” or at most 1/32” and shoot the rifle to see how far it moved the group. Then adjust a little and shoot until you get the group centered on the bullseye at 25 yards. This works best for folks who shoot in 25 and 50 yard matches and is a good starting point for longer range matches or hunting. You may find sights so adjusted will be off a little side to side at 50 yards, and if so, you just “hold” the sights or aim a little off center when you shoot, to center the group at 50 yards or further.
I wasn’t sure if I should add this last information, but decided to do so in case one has a RARE occurrence of a bore that is not well centered in the barrel. Most folks will never run into this, though. In such a case after one centers the group at 25 yards, the group will be WAY off to the right or left at 75 or 100 yards quite a few inches. In the old days as today to keep this from happening, gunsmiths and barrel makers bent the barrel to ensure the bore was straight. However in rare examples, sometimes the barrel would still shoot way off to the right or left. So what they did was take the barrel out of the stock, bend it and shoot and bend and shoot until it shot straight. I DO NOT recommend most people try this today because bending barrels is an Art Form that even many or most gunsmiths don’t know how to do properly. Normally it is best to return the barrel for replacement when this happens.
There is another option that people have done with muzzleloaders and modern rifles with fixed sights when a rifle is centered at 25 yards, but shoots 6 to 8 inches or more off at 100. Let’s say it is off that far to the right at 100. They move the sights so the group is centered a little more to the left at 25 yards so the group at 100 yards is not so far off to the right. It’s not great for shooting matches at 25 yards, but it normally is good enough for hunting small game like squirrels or rabbits when you aim a little off center at short ranges. However, on larger game like Deer, you aim center all the way to 100 yards as there is an 8 to 10 inch killing zone on deer and your group will be inside that zone from 25 to 100 yards.
Gus
Modified to add: There is no way to be certain sure how they adjusted sights in the original time period, but I THINK they did it similar to the last paragraph as it made it easy for fast shots while hunting.