Front sight filing?

[Danny Ross]

On a couple of my rifles I am shooting dead on at 50 yards but want a higher impact point. When filing the front sight approximately how much do you need to remove to raise the point of impact 1-2 inches at 50 yards? Just want a idea of how much filing I am going to need to do, so I don't have to do it all at the range (1/8, 1/4 inch, less, more?). Yeah I know if I remove to much I can't put it back on, that is why I am asking before I start. DANNY

 

[BrownBear]

The math is there somewhere if you crank in barrel length, height of rear sight, velocity of your load, and probably more. I'll leave that to the math-types, cuzz I'd rather shoot.

Sounds to me like your in the land of file a little-shoot to confirm. To get only 1-2" at 50, you're not talking about a lot, so go slow and easy with the file. Do it at the range and shoot every couple of strokes or so. I'd rather trust what I see on the target paper than math someone writes on the theory paper.

 

[Zonie]

To figure the exact amount that needs to be removed using the following formula, you have to know the distance from the front sight to the rear sight measured in inches.

I'll set it up for 50 yards.

50 yards X 3 = 150 feet X 12 = 1800 inches to target.

Next, I'll set it up for a 1 1/2 inch rise in the point of impact.

1 1/2 inches rise in point of impact = 1.500 inches.

1.50 divided by 1800 = .00083. We'll call that C for "change".

Now, knowing the distance between the sights, we multiply that number times the value of C.

Lets say it is 21 1/2 inches between the sights like it is on my Lyman GPR.

In this case we will have 21.500 X .00083 = .018 inches. That is the amount of material that needs to be removed from the front sight to raise the point of impact 1 1/2 inches at 50 yards.

18 thousandths of an inch (.018) is just a hair bigger than 1/64 of an inch.
Put another way, .018 is about the same as 5 sheets of printer paper stacked together is thick.

Oh. Writing out the formula it would look like this:

(Desired change in inches/distance to target in inches) X (Distance between sights in inches) = change in height in inches.

 

[Stumpkiller]

Soh Cah Toa. Zonie remembers.

 

[Sean Gadhar]

:hmm: Or you could take a black marker & blacken oh say 1/16" of the top of the sight blade. Then aim with what blade is below the black (that is to say use the bottom edge of the black as the new top of your sight) when you are SURE you have found the right level, just file the black off :idunno:

 

[mhb]

If you borrow a value (the sine of 1 minute of angle - .00029)from trigonometry, you only need to remember that one, and can then directly measure the sight radius (distance between sights) to be able to calculate the value of 1MOA for your sights.
Multiplying the sight radius in inches (much easier if you use decimal fractions) by .00029 will give you the decimal value of 1MOA for your sights - you only need to know how many MOA you need to change your POI to calculate how much change you need in your sight height (front or rear).
Then, knowing that 1MOA is (near enough) equal to 1 inch per hundred yards (or .250" at 25 yards, or .500" at 50 yards, etc)., you have all the values needed:
For an example, supposing an intersight radius of 30" (long rifle), and the POI being, say, 2 1/4" low at 50 yards, you would calculate that you are hitting 4 1/2MOA low at that range (2.25"/.500" = 4.5). You would also calculate that the value of 1MOA on the 30" sight radius is .0087" (30" x .00029), and the necessary sight change to bring POI to POA is .003915" (.0087" x 4.5MOA), rounded to .0039".
You would then shorten the front sight or raise the rear sight by that amount.

mhb - Mike

 

[Eric Krewson]

I am not smart enough to make complicated calculations so I take about 5 strokes with my file, shoot and see where I hit and repeat if necessary.

 

[tenngun]

Or less, since you cant put it back on once its gone. Fire 2 file repeat. "mathematic is fine but you left out a triffle, the head hands and eyes that back up the rifle" Corse you can just hold a little high...Caintukee windage.

 

[Brokennock]

You could try this. Blacken the face of the front sight (B.C. bluing pen works fine), do Zonie's math, take a fine knife edge file and file a slit/groove the distance below he top of the sight hat the math gave you. The fresh cut metal should stand out brightly, shoot using this as the top of the sight. If it is "on" either file down to it or leave as is and use top of sight for close range and the cut mark for longer ranges.

 

[Loyalist Dave]

IMPORTANT TIP for folks like myself and Mr. Krewson who go to the range, shoot & file, shoot & file, to adjust the sights. First, bring along some masking tape, and tape up the rifle surfaces all around the sight on the top half of the gun. Apply three layers of masking tape, so if you by accident with the file bump the barrel flat, or an edge of a flat, or the stock, you wont mar the rifle... you're just trying to adjust the front sight after all. Also, as you file paralel to the front sight verticle insert, you will leave a burr on either side of the sight on the filed edge. Take a second to remove that burr with the file or a piece of emory paper before you shoot. It can cause some subtle problems with your sight picture, and if you wait until you think you're finished to remove it you may find you've created "complications."

LD

 

[Roguedog]

I'm with Eric on this one. Save yourself some trouble and forget the math. Just take a file to the range with you and take a couple of small strokes with the file and shoot. Trust me, it won't take much to adjust your POI an inch or so. I did this awhile back on one of my rifles and only filed a small amount off the front sight and it was too much. Go slow!

Jeff

 

[Snakebite]

Like Eric, Tenngun and Roguedog say, just file a little bit and shoot. Easy to take metal off, hard to put back on. If you do take too much off the front, then you have to file the rear sight.

Just take it slow and easy.

 

[Eric Krewson]

I agree with Dave, I filed a bunch off my fowlers front sight a couple days ago, had to get the ball impact up 4". My barrel was wrapped with several layers of masking tape. On thing I didn't mention in my first post is that I use a very fine file for this task so a few extra strokes are necessary.

My sight is pretty low on my barrel so scaring the surrounding area was a distinct possibility.

The first time I filed a sight down on my first build I didn't tape off the area. In spite of being carful with my file it looks like a Tasmanian devil attacked the sight area of my barrel. I found it is hard to rebrown this area and get it to match the rest of the barrel, lesson learned.

 

[2shute]

You might also consider upping your powder load a few grains--particularly if you're not on the edge of overload to start with. Might solve your problem without having to file the sight.
If it does come to filing, take the advice that's been offered--file a few strokes and see what change occurs. You'll get a pretty good idea of how many strokes makes how much difference.
Good luck.

 

[Col. Batguano]

This formula was a God send when I was adjusting the sights on my new Lehigh build (34" sight radius). First few shots at the range, I was (expectedly) hitting about 4" low at 25 yards, which meant there was a LOT of metal to remove. I just set the calipers, made a scratch, and filed away until I got somewhat close, shot a few rounds, and adjusted from there. Without the measurements, I would have been too chicken to file as much off as I did.

 

[Zonie]

Many know the feeling.

As folks here know, a brand new Lyman GPR comes with the front sight intentionally left high by the factory.

Because of this, they are bewildered when the gun shoots 6-8 inches low at 25 yards. Usually they think they are doing something wrong or the gun wasn't built right.

Anyway, using the formula I mentioned above, if their Lyman is shooting 5 inches low at 25 yards they file a little off the front sight only to find it didn't make much difference.

If they would have calculated the value they would have had a equation that looked like this:

(5" low divided by 900" to target) times 21.5" between the sights = .119

If they went to a fraction to decimal equivalent table they would see that this value is almost 1/8 inch so at least they would be mentally ready to have to file off that much material.

Disclaimer You folks with new Lyman GPR's, don't use my calculations above as real numbers. Go shoot your new gun and find out just how far below the point of aim really is. Then do the calculations based on what YOUR gun actually did.

 

[Stumpkiller]

Like Tenngun said: "It don't grow back".

More than once I've gone too far. Happily Track of the Wolf has nice replacements.

 

[newtewsmoke]

Happily Track of the Wolf has nice replacements.

...that's it right there...replacing the frunt sight isn't that big a deal if one goes too far. Personally, i want my guns to shoot a little high vs. low. :wink:

 

[Col. Batguano]

:thumbsup:
How do you guys now darken that shiny silver metal that is now exposed (on dark steel front sight posts)? I've just used a little cold blue, and you can hardly tell the difference between that and the rest of the sight or barrel that is browned.

The other thing to be aware of when doing your filing, is to make sure the rear (or highest portion) you file to is indeed the highest portion you are sighting off of. If it ramps slightly upward, what ever is the highest point is what your eye will see. With my super low "Allentown" rear sight (only .22 high) and being located at a thinner portion of a swamped barrel, my front sight wound up being only .130 high above the barrel flat. Mighty low, but that's what is HC for a Lehigh. It took some getting used to that's for sure.

On most long rifle sighting radiuses, I've found that my front sight needs to be between about .02 and .03 lower (above the bore center-line) than my rear sight. On a shorter sight radius like the GPR, that number will be slightly smaller (for the same load).

On pistols the reverse seems to hold true. The front sight needs to be higher than the rear, as, due to the lessened mass, the muzzle is coming up more by the time the ball exits.

That's why it's generally acknowledged that you should find your every-day load (or most accurate combo) before adjusting your sights too much. It's a LOT easier to remove material than it is to add it!

 

[Danny Ross]

Thanks every one. Zonie one of the guns HAPPENS to be a GPR. DANNY