Front sight blade calculation help

[duckey]

I have a CZ 550 in .375 H&H Mag. The factory installed front sight hits high at 50 yards by 10". CZ sells replacement sights to correct for this and gave me a formula to figure out which one to pick from. I currently have a #7 front sight (.225") and need a taller one to bring POI down. I am also using a peep sight which has been adjusted all the way down. I have done the math over and over and nothing seems to jive with the front sight replacements on their web site. I am shooting at 50 Yards (1,800"), my sight radius is 19", I am shooting 10" high. Can someone calculate this and see what they get.

CZ offers the following from highest to lowest.

#14 .280"
#13 .275"
#12 .265"
#11 .255"
#10 .252"

[NSB]

You didn't publish the formula that they gave you so I can't help you there. Go to Brownell's and use their formula. It asks you for the distance from the front sight to the rear sight and you can go from there. I used it and it works.

[Hick]

If I'm understanding your measurements correctly, you want to come down 10" at a distance 1800 inches down range and you have 19" from front to rear sight. If this is the case, similar triangles (I teach math: think geometry: 10/1800 = x/19) says you need to increase your front sight height by a little over 0.1 inches (0.10556 to be more precise). So, you need 0.225 + 0.1056 = 0.3306. If this is what you are calculating I see your problem-- but I don't know know enough about a CZ to tell you how to fix it.

[country gent]

I used my old stand by formula error X sight radious/ distance in inches. So your error of 10" means 10" X 19" = 190" 190/1800 =.1055 more needs to be added to the existing front sight. Your existing front sight is .225 so it needs to be ( .1055+.225 ) .330 tall. The 280 may get you close. .0105 is 1" corretion with your sight radious at 50 yds. You may have to make a blade up for what you need. I have built front blades up with JB weld and filed back in to shape but they are delicate and wont stand up to any hammering ( some times heavy recoil breaks the bond even since there is very little surface area there). A pice of appropriate thickness gage stock hack saw file and drill press one can easily be made.

[duckey]

NSB...so the formula CZ gave me is....Sight Radius (19") X Impact Distance/Target distance (50 Yards converted to inches 1,800") = sight height change.
Hick... I also got the 1.0556" but it didn't dawn on me to add it to my existing sight height. I am not sure what the sight radius is exactly, where it comes from, distance between front and rear? I'll have to break out the tape measure.

I looked at Brownell's formula but I needed to know the barrell dia at front sight, rear sight barrel dia and the distance between the two. Thanks for all the help!

[Mk42gunner]

I also got .1056" for the dimensions you gave. However, I have to question the sight radius of 19 inches when using a peep sight. Is this a barrel mounted sight of some sort?

If it is a receiver mounted sight, just how short is your barrel?

I usually measure sight radius from the rear of the rear blade or aperture to the rear of the front sight blade with a tape measure. it has always been close enough for me.

Robert

[duckey]

MK42gunner....thanks for chiming in on the peep sight. My peep is receiver mounted and therefore would affect my calculations. I will measure from rear of front sight to rear of peep and recalculate. I'll prolly buy two front blade sights (one for using the iron sights and one for the peep). I'd like to be able to shoot this gun with the iron, peep or the quick detach scope to the best of its ability. I know I need a .267 adjustment for the iron sights and CZ sells a .265 so that'll be close enough. The blade sights are easily removed and installed via a dovetail with a spring type push button in front of the sight. Slight fitting of the new sights may be required.

[pietro]

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Your installation & use of a peep sight requires a taller front sight than the issue height.

There are two different ways to determine the proper front sight height:

1) Measuring the distance from the bore C/L to the center of both the front sight blade/bead, and the peep sight set to the middle of it's elevation adjustment range & comparing the differences.
(the rear/peepsight distance from the bore C/L can be measured from the center of the FP @ the rear of the closed bolt)

2) Measuring the difference between the point of aim & the point of impact @ 100yds, then calculating the chande required for zeroing.

Brownell's has a Sight Height Calculator on their website - BUT, the deviation between the POA & the POI should be measured @ 100yds for the calculator to work.

http://www.brownells.com/GunTech/Sight_Height_Calculator/detail.htm?lid=13186



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[duckey]

Well just when I think I got it. So what is FP abbreviated for, when you mentioned "from the center of the FP"?

the rear/peepsight distance from the bore C/L can be measured from the center of the FP @ the rear of the closed bolt)

I shot at 50 yards with the peep and measured 4" from POI to POA. By using the formula I mentioned earlier would I be wrong in determining front sight height if when using a peep vise installed iron sights?

[Mk42gunner]

FP = Firing Pin.

Here is the sight correction formula I use. Like any mathematical formula you can change whatever variable you need to.



Sight Correction Math

Howcan I determine the amount of sight correction needed to sight in my pistol orrifle?

A: You multiply the sight radius (in inches) by the amountof error (also in inches). You then divide this number by the range in inches.The result is the amount of correction in thousandths to adjust the sight tocorrect point of aim.

Example 1: Handgun shooting 4” low at 50 feet with a sightradius of 8 inches. 8x4=32 32 divided by 600 (50 feettimes 12 inches per foot) =.0533. The front sight needs to be lowered byapproximately .053” or rear sight raised approximately .053”.

Example 2: Rifleshooting 11" high at 100 yards withthe rear sight all the way down. The rifle has a sight radius of 17 inches.11x17=187 187 divided by 3600 (100 yards times 36inches per yard) =.0519. The front sight needs to be raised by approximately.052" or the rear sight lowered by approximately .052".

Robert

[duckey]

Thanks Rob!

Well I measured the sight radius on my rifle from Rear of front site to rear of rear sight (peep aperture) and that came out to 28 7/8" (28.88) and after calculating with a 4" error at 50 yards I came out with .064", added that to what my current front sight is (.225") and got .289". So the tallest sight CZ offers is a .280" which should be close enough. The dia. of the barrel on my rifle is not easily measured as there is a big chunk of metal machined in with a dovetail that the rear express sights fit into and that is about an inch or so long. I'll try a .280 front sight and see where that puts me on paper at 50 yards then on out to 100. I suppose I could figure out where POI would be at 100 yards with a bit of math without taking it to the range. Anyhow, Im getting warmer. Thanks for your help.

[44MAG#1]

It's really pitiful.

10 divided by 1800 times 28.875 equals what you need if the rear sight is bottomed out.
Now one will want to have some leeway to adjust the rear sight up and down so with the rear a few clicks up to allow some leeway. Shoot the gun again. It will be shooting higher than 10 inches now. Then divide the amount it is higher by the distance time the 28.875 inch sight radius equals what you need.
This is a simple thing to figure.
You said in the first post the sight radius is 19 inches now it's 28.875 inches. Which is it?

[duckey]

I'll never claim to be a math wiz, doesn't come quickly for me like 44MAG#1. We all have our weaknesses.

The sight radus is 19" for the factory sights. The peep sight, sight radius is 28.88".

[44MAG#1]

I'll never claim to be a math wiz, doesn't come quickly for me like 44MAG#1. We all have our weaknesses.

The sight radus is 19" for the factory sights. The peep sight, sight radius is 28.88".

Sorry to inform you as I am not a math whiz. I know very little. But I do know 3 maybe 4 things.
Maybe on my best day 5 or 6 things but that is stretching it.

[Geezer in NH]

Target is the true way IMHO measurement may get you close when done correctly but shooting will tell exactly with no problem.

[pietro]

The dia. of the barrel on my rifle is not easily measured as there is a big chunk of metal machined in with a dovetail that the rear express sights fit into and that is about an inch or so long.




The rear sight restricts a barrel diameter measurement only if the attempt to measure the O.D. is done in a vertical plane...............


The barrel's diameter should be consistent at whatever angle it's measured, so it's fairly simple to measure in a horizontal plane, or some other plane that avoids the rear sight/base.

The open/iron sighted barrel's rear sight height should be 50% (half) the bbl O.D. @ the rear sight, + the height of the rear sight blade in the middle of it's vertical adjustment range (to allow for zeroing).

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[rpludwig]

As others have said, use the math to get in the ballpark, leave some wiggle room to file away or adjust to POI with your loads.

I have a trapdoor shooting mighty high (as most all do with smokeless loads) that's about to get that treatment. Xtra tall front is installed, with math/file/dremel at the ready when weather cooperates.

[44MAG#1]

What has barrel diameter got to do with these?
No point in making something difficult out of this.
He needs a taller front sight.
How much taller is easy to figure.

[pietro]

What has barrel diameter got to do with these?
No point in making something difficult out of this.
He needs a taller front sight.
How much taller is easy to figure.


There can be diametrically different end results from knowing what to order, and thinking a calculation might be spot-on.


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[44MAG#1]

Again, he needs a taller front sight.
No use in trying to turn this into a mental exercise.
By using a taller front sight the impact will be lower.
He needs to figure out how tall the front should be.
That is done mathematically by knowing how high the gun shoots at a given known distance and the distance between (sight radius) his sights.
We are dealing with angles here.
Nothing more nothing less.

[pietro]

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http://i.imgur.com/WTDnnwE.gif

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