Adjusting Sights on GP 100**Updated with Sight Specs**

[forrest r]

10 yards. With it cranked all the way down I’d say 1.5-2” high. Next time I shoot it I’ll measure it. It was cold today. Might get out there again on Friday.

That's a ton of adjustment for 10yds!!!

Here's a formula to figure out how much movement/height/ect you'll need to get on center.

9 x (2"/360") ='s .050" (50/1000th of an inch)

9 ='s the distance between your sights. You'll have to measure your gp100 to get the actual distance.
2" ='s the amount high/low/left/right of center
360" ='s the # of inches to the target (10yds ='s 360")

That's a lot considering you need another 50/1000th's of movement after your sight is all the way down.

Typically with firearms I center the rear sight left/right and center the rear sight up/down and shoot groups @ 50ft. Then I measure how far off my poi is from my poa and use the formula above to figure out just how much is needed to adjust the sights to get to the poa.

The high/low of a load never really bothered me unless it was drastic. Shooting hot 110gr/125gr bullets in a 357 compared to 158gr bullets. I'd expect to see the lighter bullets hitting low. Now if the 158gr bullets were hitting extremely high/low I'd consider that drastic.

Extreme left/right movement of the sight on the other hand I don't put up with. If the firearm is that far out of spec I either fix the firearm or it goes down the road.

Next time you go to the range try centering the rear sight left/right and up/down and use the formula above to see just how much you need to move the sights to where you can hit the poa. Up & down is a simple sight swap using that formula above will tell you the sight height you need. This will put your poi to the poa and leave your rear sight centered up/down for adjusting other loads.

Left/right on the other hand is a lot harder to correct if it's too far of the centering of the rear sight.

 

[sabbfan]

Yes. The rear sight. I never touched the front sight.
Take the rear sight out and file along the top? Wouldn’t it be likely it wouldn’t be even?

I laid the file flat on the table and held the blade on top of the file, that way it came out level.

 

[Homerboy]

I went back today to try again. I am still shooting high. Cranked it all the way up and brought it down bit by bit. With it bottomed out as low as it will go, I am hitting a good 3 inches high. Even with a 6 o'clock hold. My H-Viz sight is .about .319 inches. The Dawson Precision sight says I need a .356" sight, but I confess I didn't bring a tape measure. I guess I'll go back one more time and measure right.

I also brought my S&W 67-4 with a 4" barrel. I was hitting high with that, also, and elevation was also cranked all the way down. Again, this was all with a pistol benchrest. I have a older Model 15 with Pachmayr's. Maybe I'll bring that and the Ruger for one more test and see if I hit better with the Pach's.

I have no idea how tall the Ruger Hi-Viz sight is. It doesn't list the specs on their website.

 

[sabbfan]

Keep in mind shooting off a bench will usually not have the same point of impact as shooting offhand, the recoil is not handled the same way causing it to hit differently.

 

[Homerboy]

Keep in mind shooting off a bench will usually not have the same point of impact as shooting offhand, the recoil is not handled the same way causing it to hit differently.

Yeah. I always suck shooting at paper too. I shot offhand and a spot of mulch in the backstop and was pretty consistently hitting it.

 

[Homerboy]

OK, so I measure the factory sight. The height of the sight flush off the barrel, the part sitting on the base which goes into the groove, is roughly .280. I had to subtract the height of the base. With the sight installed, the base is perfectly flush with the barrel. The whole hieght with the base is .350".

The Hi-Viz is almost exactly the same. Height of sight off the base is .276. Height of whole sight is roughly .350.

The Dawson sight says to measure from the slide or barrel. That wouldn't include the base. So the Hi-Viz being.275 from the base is the number I should be working with? Using the .275 high number and three inches high at 10 yards, Dawson is saying I need a sight .336 high. That would certainly be higher as you say I need, but why would the factory sight also be so much shorter than what I need?

I am shooting from a rest in single action. I am shooting my 158 grain SWC reloads. I have some factory .38 lying around but the gun will be almost exclusively shot with my reloads, so I want it to be dialed in for those. I am not flinching. I have been shooting a long time, but I tested myself by loading some spent shells in there. No flinch on a click.

So the new sight is the same height as the factory. Could it really be that far off? I'm gonna shoot it again on Monday or Tuesday to get an actual measurement, and plug the numbers into the Dawson calculator, but can 3-4 inches high from a rest at 10 yards be fixed by a slightly taller sight?

 

[WrongHanded]

but can 3-4 inches high from a rest at 10 yards be fixed by a slightly taller sight?

Yes. Because it's based on a ratio.

You're shooting 3-4" high at 10 yards. But 10 Yards, is 30 Feet, which is 360 Inches.

Let's say you're shooting exactly 3" high over a distance of 360".

3 ÷ 360 = 0.0083.

Multiply your sight radius (let's say it's 7" to keep it simple) by 0.0083, and that gets you the difference in sight height. 7 × 0.0083 = 0.0581.

In this crude example, your front sight would need to be 0.0581" higher.

It's worth considering, that if you get a front sight that is exactly the right height to make your reloads hit POA at 10 yards with the rear sight all the way down, you will only have elevation adjustment in one direction. So, in my opinion, it's better to turn the rear sight up a half or a full screw rotation before you get the final numbers for your new front sight. Personally, I prefer to take the rear sight up from bottom a half turn when doing this.

 

[Homerboy]

Yes. Because it's based on a ratio.

You're shooting 3-4" high at 10 yards. But 10 Yards, is 30 Feet, which is 360 Inches.

Let's say you're shooting exactly 3" high over a distance of 360".

3 ÷ 360 = 0.0083.

Multiply your sight radius (let's say it's 7" to keep it simple) by 0.0083, and that gets you the difference in sight height. 7 × 0.0083 = 0.0581.

In this crude example, your front sight would need to be 0.0581" higher.

It's worth considering, that if you get a front sight that is exactly the right height to make your reloads hit POA at 10 yards with the rear sight all the way down, you will only have elevation adjustment in one direction. So, in my opinion, it's better to turn the rear sight up a half or a full screw rotation before you get the final numbers for your new front sight. Personally, I prefer to take the rear sight up from bottom a half turn when doing this.

I agree with setting the elevation now to a half to a full turn to give me some adjustment for different loads.

So I should raise the rear sight say a half turn, and shoot for the target. Get an accurate measurement, and plug those numbers into the Dawson calculator. But the height of the sight does NOT include the base, so the .350 measurement of the whole sight is irrelevant, and the .276 from the base up is what I should worry about? That's what Dawson says, I just wanna be sure.

Thanks very much!

 

[WrongHanded]

So I should raise the rear sight say a half turn, and shoot for the target. Get an accurate measurement, and plug those numbers into the Dawson calculator. But the height of the sight does NOT include the base, so the .350 measurement of the whole sight is irrelevant, and the .276 from the base up is what I should worry about? That's what Dawson says, I just wanna be sure.

Thanks very much!

If Dawson measure from the top of the barrel to the top of the sight, you must also do that. The good news is that if you set the rear sight up a little (as we discussed), if you don't get a perfect measurement you will have some wiggle room.

 

[Homerboy]

If Dawson measure from the top of the barrel to the top of the sight, you must also do that. The good news is that if you set the rear sight up a little (as we discussed), if you don't get a perfect measurement you will have some wiggle room.

OK. I got to the range and turned the rear sight, that had been bottomed out, up one half turn. Both the factory sight and the Hi-Viz I have were measuring about .273". Here's a pic of my target. 10 yards from the bench. The two shots further down are my fault. I forgot my pistol rest so I was using my range bag. It sagged a few times. The four on the top are between 2.75 and 3 inches from the bullseye. I used 2.75" high for the calculator and it told me I need a sight .325" high. Closest to that they offered was .330, so I ordered that.

 

[WrongHanded]

OK. I got to the range and turned the rear sight, that had been bottomed out, up one half turn. Both the factory sight and the Hi-Viz I have were measuring about .273". Here's a pic of my target. 10 yards from the bench. The two shots further down are my fault. I forgot my pistol rest so I was using my range bag. It sagged a few times. The four on the top are between 2.75 and 3 inches from the bullseye. I used 2.75" high for the calculator and it told me I need a sight .325" high. Closest to that they offered was .330, so I ordered that.

View attachment 911281

If you call them, they'll make whatever you want. I don't think it even costs extra. Or you can take what you ordered, try it, and if it's still not right they will help you out for free (they have a guarantee).

 

[Homerboy]

If you call them, they'll make whatever you want. I don't think it even costs extra. Or you can take what you ordered, try it, and if it's still not right they will help you out for free (they have a guarantee).

Would there be a big difference between the .330 and .325 as far as accuracy?

 

[WrongHanded]

Would there be a big difference between the .330 and .325 as far as accuracy?

Accuracy? No. It may just mean you have to adjust the rear sight up a little more.

 

[Homerboy]

Accuracy? No. It may just mean you have to adjust the rear sight up a little more.

Thanks. But since I have wiggle room both ways maybe that’s best. You say they’ll exchange if I need to?

You’ve been very helpful. Thank you. Most of my revolvers have been fixed sighted. Never really had to deal with this. But I’m learning!

 

[WrongHanded]

You say they’ll exchange if I need to?

You should check their site for details, but from what I recall, they offer one free replacement front sight to correct for any POA/POI inconsistencies, if the front sight you bought doesn't work out.

 

[Homerboy]

You should check their site for details, but from what I recall, they offer one free replacement front sight to correct for any POA/POI inconsistencies, if the front sight you bought doesn't work out.

thanks. The .330 is ordered. If it’s not what I need I’ll reach out to them. I’ll let you know how the new one works. You’ve been very helpful. Thanks again.