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Advice On Opening the Rear Notch

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tomd999
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Post by xmastershooter Thu Mar 28, 2024 6:08 pm

First topic message reminder :

I finally decided to work on this project of widening the rear notch of an Elliason iron sight from a Gold Cup. I found the perfect file with the smooth safe edge. I also smoothed down this safe edge with another file to avoid little gouges onto the bottom corner edges of the rear sight. Hopefully, only the sides of the notch will be touched. Thanks to SteveT for his observations.

The front sight width is .115" and the rear notch opening is .130", cut at a slight angle.  My eye to the front sight is 32" and I know this is relative to each shooter's perception to the judgement of the the left and right gaps. However, for a general guideline, would our shooters let me know their rear sight widened dimensions after the "operation?" Or better yet, how much wider was the notch as compared to before the procedure?  The later question may then apply to any pistol.

Many Thanks,

Norman

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Post by John Dervis Sun Mar 31, 2024 3:05 pm

targetshooter_10x wrote:To all of the other iron sights shooters out there.  How does Normans image compare to your sight picture?  

My rear notch is not quite that wide so I see less daylight.  Shooting outside without cover (Camp Perry) I will see more light.  Under cover (everywhere else I shoot) I need to open the rear notch just like you are asking.  The image Norman posted would look like a good place to start and might be all I would need.

John

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Post by xmastershooter Thu Apr 04, 2024 9:30 am

Update on sight picture: This would be a more accurate representation when the front sight post and gap heights were adjusted properly. I also drew a couple of faint pencil lines to simulate the spacing with my original stock notch gap. This spacing is only 1/3 of what we see in the drawing. To put all this in perspective, take a look from 25 yards using the full size drawing.

The big surprise as John (mathematician targetshooter) and I worked on JB's updated parameters with his service pistol while using the spreadsheet to determine the "optimal gap", it showed .138" which was the womped-out notch width JB found to be ideal. Of course, this would work for a couple of shooters and perhaps many more, but it's something to think about. The forum is fortunate to have a couple of consultants on this subject.


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Post by john bickar Thu Apr 04, 2024 1:18 pm

xmastershooter wrote:The forum is fortunate to have a couple of consultants on this subject.

I like how we have people with advanced degrees and full careers worth of experience in this field and my main contribution has been a very redneck, "I just womp it out."

You can take the boy out of Ohio, but you can't take the Ohio out of the boy. Laughing
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Post by targetshooter_10x Thu Apr 04, 2024 4:05 pm

john bickar wrote: "I just womp it out."

You can take the boy out of Ohio, but you can't take the Ohio out of the boy. Laughing

I love this quote! As a (hopefully) humble student of all of the Masters that have come before me I can't tell you how much I appreciate your wisdom and intuition here. As someone who grew up shooting international events and iron sights I have a passion for the purity of the "old skool" way of shooting. I have always wondered "What does that person 'see' when they are looking down the sights?" I also needed something just slightly more quantifiable than a "womp" when talking about a rear sight notch. Enter the HS math, a spreadsheet, and some help from the various forums.

I think at the end of the day all of this comes down to "personal fit" and what works for you and your "eyeball" as we try to keep the sights still at the end of our arms while not messing up the picture pressing the trigger, and breaking the shot.

Our friend fc60 would say. "Show me the 'target'" So I will attempt to offer up my work in a way that will help the next person asking "how big should my front sight or rear notch be?"

Thank you Norman (xmastershooter) and John for all of your help, measurements and artwork.
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Post by targetshooter_10x Thu Apr 04, 2024 5:32 pm

Here is an effort to "show my work".  Disclaimer:  this is not meant to be 'financial advice'.  Do your own due-diligence.  What works for me or Mr. Bickar might not work for you.  

Measurements needed for calculations with some examples:  
A) Distance from eye to rear sight: 24"
B) Distance from rear sight to front sight": 7"
C) A + B : 31"
D) Width of rear notch: 0.138
E) Width of front post:  0.132

Angles
1 Radian = 57.29582791 Degree

Now the Math: Trig and Algebra

Measuring the angle from the eye to the rear and front sight.
F) Angle from eye to notch:  tan( D / A ) = 0.005750063371 Radians
G) Angle from eye to front post:  tan( E / C ) = 0.004258090251 Radians

H) Inches to target:  900 ( 25 yards )
I)  Black Rapid Fire circle: 5.5"

What is perceived at the target?
J) Rear notch:  tan( F ) * H = 5.175"
K) Front post:  tan( G ) * H = 3.832"

L)  Amount of "light" expressed as a percentage of the rear notch: (( J-K ) / K) * 100 = 25.95%
M) Each side of the front post:  L / 2: Approx 13%  

Advice On Opening the Rear Notch - Page 2 Sub6_h10


So how big do I need to make my back notch?  
N) The radians or angle that express the "desired light" is F-G = 0.001506 ( ~26% in our example )
This number is the angle represented by the rear notch minus the angle of the front post. Resulting in the angle of the "light".

O) Recommended notch:  tan( G + N ) * A = 0.138"  aka "1 Womp"  


If you made it this far.  Congratulations.   Good luck, and may you be one of the next Presidents 100.


p.s:  There are many schools of thought out there regarding the sight picture.  There are other recommended ratios out there a 1:1:1 ratio and the 1:2:1 are a couple that Don Nygord talks about in his notes.  
Here are the ratios in terms of percent of "light bar" like I talked about above.  
1:1:1 = 33%
1:2:1 = 25%  ( Russian golden ratio )
1:3:1 = 20%
1:4:1 = 16%
1:5:1 = 14%
1:6:1 = 12.5%
1:7:1 = 11.1%
1:10:1 = 8%
1:18:1 = 5% ( Out of the box Bomar @ 25" from your eye )

The above example is between the 1:5:1 and 1:6:1 ratios.

p.p.s:
I have personally found that a 1:2:1 ratio is just WAY to much light for me and the front sight get's lost in a sea of light.  That is especially true on well lit ranges and outdoors on a sunny day.    Also the flip side is also true.  A 1:18:1 ratio is difficult to pick up the front sight again on sustained fire and is especially hard to see in poor lighting conditions.  My personal "sweet spot" is right around 13% on both sides.
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