Trigonometry sight filing question.

S

stubbicatt

New member
Guys I have one of the S&W 22-4 revolvers. Really a pretty gun. Problem is it shoots way low. I called S&W and they sent me a replacement sight blade for it, but near as I can tell, it is exactly that, same sight blade. I had hoped they would send me one properly regulated for the piece, as I had asked them to do.

So I reckon to start filing the front sight down so that it shoots to the point of aim.

Question is: whether there is a method of determining how much to file off of the blade using Trig or the like? I suspect in the end I'll take a file with me to the range and start whittling down the front sight, a little at a time until it shoots to the point of aim.

Suggestions?

Oh. And what sort of file would be the tool of choice I wonder?
 
what bullets weight are you using? I suspect that if you are using a bullet "lighter" than the standard weight and velocity it probably will shoot low if you are using a lighter bullet
 
230 grain ball, and 200 grain SWC. I suppose I could start by lowering the powder charge? Longer barrel time and all that might bring it up?

I hadn't thought to do that...
 
I think with fixed sights it is best to stay close to standard loadings. when you start filing sights things can go wrong. I'm not convinced that the same person sees the sights every time just because of different lighting conditions.
 
Much better to play with the powder charge but they you never stated what it is nor what distance you are shooting and a measurement of way low.
 
To correct your sight height at 25 yards take your sight radius in inches times the point of impact from your aiming point in inches and divide that by 900.

Best Regards
Bob Hunter
 
BTW. I've found that to bring up the point of impact, a heavier charge is needed... the additional recoil brings the muzzle up, not a longer time in the barrel, with a reduced charge, at least in my experience...
 
Bob's calculation is the result of similar triangles...

If it's 8 inches low at 10 yards (assuming a 6-inch sight radius, about right for a 4" barrel), then

8 inches / 360 inches = x / 6 inches

x = 6x8/360 = 48/360 = 0.13 inches (~1/8 inch) needs to be filed off the front sight. You can change this calculation for the exact value of your sight radius (distance between front and rear sights).

This assumes you will always be using the same ammo, however. The gun will likely shoot higher with a heavier bullet, all other things equal. You will want to make the adjustment using "typical" ammo and learn to understand the reasons for shooting high/low with other ammo.
 
For sight correction I believe you will be better served by using a 25 yard sight in.

Doing so, using spacecoast numbers 6x8=48 48/900 you will only have .053 of correction, this is less then 1/16 of an inch.

However if you are never going to shoot farther then 10 yards with your handgun then using 360 as your constant to divide by is correct.

Best Regards
Bob Hunter
 
Good point, you'll minimize measurement error at 25 yards. I'd recommend several stages of cut and try. It's easier to file a bit more off than to put it back on if you go too far.
 
Unless you have done your seven year apprenticeship as a gunsmith or machinist, you might have trouble filing a sight blade flat and square freehanded. The setup I saw had a long flat file with a piece of sheet brass soldered or epoxied to about half its length. Put the file on the bench, put the gun on the file upside down with the rear sight flat on the brass. Stroke to file the front blade evenly.

Me? I just visited my gunsmith, he does it on a milling machine. I had one with a calculated correction of .023". He said "Let's take off 15 to start with and you bring it back by if it needs more." He cut it .015 which worked out fine, the computed value not needed for a good zero.
 
7 to 10 yards, about 6 to 8 inches low.

And I have that replacement blade in case things go wrong...
Click to expand...

Stubbicat,

So at 7 yards you are shooting 6" below point of aim.

Just to be sure about something let me ask:

Does it shoot that low at that distance with factory ball ammo consistently?

Two, does it also shoot this way when another shooter shoots the gun?

My recommendation...

Set the sights with factory standard velocity ball ammo. This means from a major maker, Federal, Winchester, etc.

Set the point of aim/point of impact to your tastes for at least 15 yards (25 yards is preferable). Use a rest to do this.

Lower the sights by removing .010 at a time. File a bit, try shooting, file. Repeat as needed.

tipoc
 
Aha. So today on a beautiful sunny day, I went to the National Forest and brought my revolver. I started shooting at bits and whatnot at about 25 yards, and further out, and even as far as what looked to be about 45 yards I was hitting a frisbee with regularity, so long as I did my job and stayed behind the sights and followed through.

Seems like someone else here said, it is probably sighted in at a greater distance, and that seems to be the case.

I'm not filing, machining, or messing with anything, as it was a greatly satisfying plinking experience at 25 yards +.

The double action is really nice. I did detect that there was one moon clip it didn't seem to shoot as smoothly with, and sure enough when I got home, and laid it on the counter, it was a little bit bowed. I sort of bent it with my hands to where it was as level as I could detect. I wondered why it got that way, when I remembered that it was the same clip I loaded up by hand rather than using a moon clip tool. It is my unverified belief that I bent it when mashing cartridges into it with my thumb. I guess even if it is a spring steel clip, it can be deformed if not loaded properly.

In all I am altogether satisfied. Now if only I would get out and shoot more than once every six months or so. I had nearly forgotten how much fun it can be to plink in the forest.

Thanks to all who chimed in here. It is merely a question of holding over a bit at closer distances.
 
Before filing anything, re-read your post #3, which is on the right track. Start with keeping the load as close to the standard .45 ACP as possible and see what happens. With handguns, barrel time is critical. Recoil begins the instant the bullet starts to move and the longer it takes for the bullet to exit the barrel the higher the gun will have risen. Conversely, a fast bullet will exit the barrel before the gun has risen far enough for the sight to be at the point of impact.

Jim
 
One would think it would be best to use factory ammo to sight in a gun being they have a greater repeatability with charge weights.
 
When all the Dust settles here:

SiteAdjust(in) =
MissDistance(in)*SightRadius(in)
..........[RANGE(Yds)*36]

EXAMPLE:
Range: 25 Yds
Sight Radius: 5½ inches
Miss Distance: 10 inches

Adjust sight: 0.061 inches (1.5mm)

.
 
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I guarantee you... that factory ammo does not have a more consistent charge weight than what I can hand load
Click to expand...

Well maybe but it ain't your hand loads we're talking about :)

Gentleman gets a new gun. He takes it out to shoot and reports that at 7 yards it's shooting 6" below point of aim. So he decides the sights need replacing. Some bright fella asks what's he shooting? He says...

230 grain ball, and 200 grain SWC. I suppose I could start by lowering the powder charge? Longer barrel time and all that might bring it up?

I hadn't thought to do that...
Click to expand...

He's shooting his own handloads.

So another fella opines as he may want to shoot a few boxes of factory 230 gr. ball at the usual 850 fps or so from a 5" barrel. If he shoots some of this he can have a baseline to work off of with that gun. Or he can chase his own tail for awhile.

tipoc
 
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