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Advice On Opening the Rear Notch

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Post by xmastershooter 3/28/2024, 7:08 pm

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 xmastershooter 3/28/2024, 7:13 pm

Correction......due to a senior moment,

the rear notch is .115 and the front sight width is .130"

Norman

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Post by Tripscape 3/28/2024, 9:12 pm

Nirman,
People may say whatever it feels best to YOU. However, in a perfect world watch this video. I understaand the bullseye and issf are different practices, but these people know their proverbial "sh!t".

https://youtu.be/-ywzAjeBnwM?si=XdK6FsBa0xRVSkOU

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Post by Dulcmrman 3/28/2024, 10:21 pm

Tripscape wrote:Nirman,
People may say whatever it feels best to YOU. However, in a perfect world watch this video. I understaand the bullseye and issf are different practices, but these people know their proverbial "sh!t".

https://youtu.be/-ywzAjeBnwM?si=XdK6FsBa0xRVSkOU
Great video!  It illustrates that "sight alignment" is far more important than "sight picture".  When I modified the rear sight on my Giles .45 I filed a bit off of each side of the sight until it "looked right" to me.  I did not measure the width.  Rather, I widened the notch until I had light on each side that my old eyes could easily discern.

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Post by targetshooter_10x 3/29/2024, 2:08 am

Greetings Norman,

I spent a lot of time one weekend with my old High School trigonometry books and figured out how to get all of my iron sights pictures looking the same from my free pistol down to my 1911.

The moral of the story I learned is that sight radius and distance to front sight are the biggest factors in determining "optimal" rear notch spacing.

Based on your description above we have similar dimensions and so I can comfortably share my results with you for reference. You mileage may vary.

The dimensions for my 1911 with bomar sights ended up like this.
Eye to front sight: 32"
Sight Radius: 6.7"

Original:
Rear notch: 0.116" Front Sight: 0.130"

Modified:
Rear notch: 0.144" Front Sight: 0.130"

For me this best matched my ideal sight picture that I had on my Hammerli 280 that used identical 0.142" front sight and 0.142 rear notch with a 8.7" radius.

If you are interested I can work with your measurements for you and it will give you a perceived dimensions at 25 and 50 yards you can draw on a target.

Hope this helps.
Cheers,
John
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Post by Froneck 3/29/2024, 9:27 am

If you intend to open the rear sight notch width get fine flat Needle File with no teeth on the edges, then the bottom of the notch will not be filed. Some files have only one edge smooth so only use the smooth side on the bottom. When filing have the file at an angle, the rear side of the rear sight (eye-side) should be  less in width that the far side. Straight sides will cause shadow. Front sight the same, eye-side should be wider than muzzle side. Rear sight angle change can be seen on quite a few factory rear sights, an endmill wider than the width of the notch cut just enough so the notch sides will be knife edged. As mentioned above the cut angle by the file will do the same thing.

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Post by john bickar 3/29/2024, 10:14 am

Ha! When I picked up your guns the other day at the range my first thought was "dang that's a narrow rear sight notch."

I normally just eyeball it. I "womp out" the rear notch on all of my 1911 iron sight pistols. My thought is, you're just eyeballing it when you're shooting it anyhow, so precise measurement is not necessary. A crisp vertical on both sides is important, though.

I can mic my service pistol rear sight to get you an idea of how wide it is.
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Post by Froneck 3/29/2024, 10:45 am

I might add that width of rear sight notch depends on the width of the front sight. I addition the distance between the front and rear sight should be considered if a Long Slide is used of if like some of those 1911s years ago that had front sight extended beyond the muzzle.

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Post by xmastershooter 3/29/2024, 11:30 am

Hi JB,

I'd like to see your pistols someday to look at your "womped out" rear notches. Your measurements may will give me a head start.

BTW folks, JB shot a fantastic Standard Pistol score recently.

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Post by xmastershooter 3/29/2024, 11:43 am

Hi Froneck,

Thanks for your hints. I started last night with my filing using a very fine file.

I started with 10 passes using the file to the right and left sides of the notch.  The opening started at .115" and it measured .115" afterwards. OK, didn't want to rush things so I filed 10 passes to each side again with the result at .115" AGAIN. What a WUSS!

Now I know it wouldn't harm anything by putting more pressure with the file. After 30 passes to each side of the notch, the opening went from .115" to .122" which was a noticeable difference to the sight alignment picture. To be continued after digesting the replies on the subject.

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Post by tomd999 3/29/2024, 12:09 pm

Hiya,

Unlike a lot of shooters I have a machine shop in my garage so here’s what I do to cleanup/widen sights. I use a 3/32 carbide end mill for the rear sight slot, that’s about 90 thousands wide so you have to be very careful on speed and feed when you’re cutting. I set the slide in the vice and true up Y on the rear face of the blade so X is a clean 90. Then I set a 3 to 5 degree angle for each side on the vice depending on the blade thickness so when the blade is cut, the rear face of the sight blade is the narrowest part of the notch looking from above, this way there is no refraction of light from parallel sides in the notch. Don’t forget to touch up the surfaces with cold blackener solution as the cuts will be reflective and prone to oxidation. Any gunsmith will a mill can do this type of mod so if your shy to take a file to your sights, this is an alternative.

I would note that I’ve seen a sight blades that have a shallow depth, my S&W 41’s and 52’s being particularly shallow. I have taken all of mine down to make the sight picture more like a typical BoMar 1911 look. 

For front sights, I also taper them at 5 on the sides and put an ascetically pleasing taper from rear to front on the top surface and undercut the rear face 10 degrees, this assures that the rear face of the front site is the tallest and widest for a nice sharp image in the rear notch with no glare. 

If you use spray can sight black, remember to brush it off before reapplying as it does layer and close up the sight picture, carbide smoke doesn’t leave as thick of a layer.

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Post by chiz1180 3/29/2024, 12:45 pm

Just some food for thought, you can replace the sight if you go too far. Take your time with small bites, take some notes, remove more if needed. If you go too far, get a new sight.
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Post by xmastershooter 3/29/2024, 12:59 pm

Hi John (Targetshooter_10x),

I've noticed the Bomar, Elliason and Marvel .22 conversion have similar dimensions for the front sight widths and the rear notch widths, that is, the front sight widths are significantly wider than the notch widths.

I also noticed that the H208s and AA Marvel .22 conversion have similar front sight widths when comparing to the notch widths (although the sight radius of the H208s is almost 1 1/2" longer.

With all the variations of pistol sights, it is impossible to quantify measurements to the sight picture appearance. Perhaps a better way to imagine the appearances of the spacing would be to assign a fractional number to the components. For instance, that great video posted by Triscape show the each spacing of the left and right front post to the notch would be about 25% of the front post width. Also the spacing to the bottom of the bullseye is also 25%.

I've heard shooters talk about a "line of white" but I'm curious to the fractional spacing when comparing the front sight widths. I would appreciate any inputs. I'm especially curious what John can estimate the .144" notch opening would look like. I wish that we can have interchangeable rear sights with different widths to evaluate. Once we open up the notch too much to evaluate, I guess the rear sight can be replaced if the part is not discontinued or near impossible to get.

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Post by Sa-tevp 3/29/2024, 1:41 pm

If you get a chance to handle a Euro Air Pistol, 50 Meter Pistol or Standard/Sport/Rapid Fire pistol most have rear sights with adjustable notch for width and height, and front sight blades in different widths and heights. It may give you a quick idea on where you want to get to for sight picture.

(...and yeah, I have had to replace a Bomar style rear sight that I opened up too much.)

Steyr rear sight:

Advice On Opening the Rear Notch 100508884_18376_AE80202B9EE5FA37
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Post by Froneck 3/29/2024, 2:07 pm

That video on sight notch is OK for international shooting since it's all at one distance. NRA and CMP matches are at 2 distance, 3 if you include the gallery match. I think sight width is what the shooter likes and why adjustable width sights are available. Easy way to correct making the rear notch too wide is have the front sight replaced, lot cheaper than replacing the rear unless it the simple GI 1911 type.

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Post by targetshooter_10x 3/29/2024, 2:16 pm

Greetings Norman.

I had the same thoughts as you when I set out on my quest.  "What is the ideal amount of light?".  After watching the same videos and seeing the perceived 25 percent on either side I was convinced that was too much.    So upon measurements and calculations on my Hammerli.   I found that 25 percent was the total white that was divided in half.  12.5 percent on each side of the front sight.     I also shoot a sub six hold and that is the gap I shoot below the black.  

However this is only 1/2 the battle as sight radius and distance from your eye to the front sight and rear notch come into play.   You can imagine the infinite combinations of arm length and sight radius possible.    As mentioned, long slides, extended front sights past the muzzle, sight manufacturers...  etc.  

On my first attempt to reconfigure a bomar I eyeballed it and got lucky with 13 percent light on both sides shooting one handed.    Surprisingly if I took the same gun unmodified and held it 2 handed the sight picture was perceived as the almost perfect end result.   Since we are a rare breed I believe the manufacturers know this and market for the masses shooting 2 hands.  

So armed with this information and some calipers I started measuring all my pistols.    I went on a trek to figure it all out with some math and equations gleened from the forums I put together some calculations that placed our 3D puzzle into a 2D "perceived" image.  

This I believe is what all the intuitive amazing shooters are saying when they "womp out" the rear notch.   I didn't have all of the tools or time to do the work myself so I had to be able to tell a trusted gunsmith my desired width.  

For me the 0.144 rear notch at 25 inches from my eye looks like 10" at 50 yards and 5 inches at 25 yards.  If you use the rear notch as a "caliper" and drop the front sight.  The 50 yard black is perceived smaller than the 25 yard black which is perceived as quite a bit bigger relative to the rear notch.  

I have a spreadsheet that I made that isn't ready for prime time but I'm happy to plug in some numbers for you if you can give me your distance from your eye to rear sight,  distance from front sight to rear sight, and front sight width.  

Looking at your previous message.  Your front sight is 32" from your eye and 0.130.  All I need is the distance from your front sight to rear sight.   

Cheers!
John
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Post by john bickar 3/29/2024, 2:17 pm

My service pistol sight measurements:

Rear sight notch: 0.138"
Front sight width: 0.132"
Sight radius (rear of front sight to rear of rear sight): 7"

I don't know the distance of my eye to the front sight. You're actually one of the only people who might have that measurement. You know my build and can probably approximate it anyhow.
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Post by xmastershooter 3/30/2024, 9:09 am

Your front sight is 32" from your eye and 0.130.  All I need is the distance from your front sight to rear sight.  
6 5/8".................thanks!

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Post by xmastershooter 3/30/2024, 9:23 am

john bickar wrote:

My service pistol sight measurements:

Rear sight notch: 0.138"
Front sight width: 0.132"
Sight radius (rear of front sight to rear of rear sight): 7"

I don't know the distance of my eye to the front sight. You're actually one of the only people who might have that measurement. You know my build and can probably approximate it anyhow.

Thank you for your input. This says a lot about JB, from an unassuming national champion. "Mr. Iron Sight!"

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Post by targetshooter_10x 3/30/2024, 10:56 am

Good morning Norman, 

Based on my calculations you can do a couple of "art projects" with a sharpie, or some postit notes on a target.  These are the perceived widths you will see imposed on the target looking thru the sights. 

25 Yards: 
Front Sight: 3.66" wide ( 0.130 ) :  3.66  inches. 
Rear Knotch Unmodified ( 0.115) :  4.09 inches
Rear Knotch Modified: ( 0.141 ):     5.01 inches 

50 Yards:  Double the above numbers 

The above numbers are 5% of the rear notch on either side of the front sight unmodified and 13.5% on either side modified. 

I would be interested to hear what you think. 



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Post by xmastershooter 3/31/2024, 9:44 am

Advice On Opening the Rear Notch 20240316


Haven't sent a picture in a long time. My preview seem to look too large.

This would be an accurate representation of your dimensions. Thanks for your great help and welcome to the forum. I'll be sending a PM.

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Post by targetshooter_10x 3/31/2024, 2:05 pm

Norman. That looks fantastic. That is almost exactly what I would expect to see for myself with a 6 o'clock hold.

Those other dimensions you sent me in PM
I'm too new to the forum and can't respond to a PM yet.

Those perceived dimensions at 25 yards are:
4.78 rear notch and 3.60 front sight
12.3 percent light on both sides.



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Post by targetshooter_10x 3/31/2024, 2:07 pm

To all of the other iron sights shooters out there. How does Normans image compare to your sight picture?
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Post by john bickar 3/31/2024, 2:09 pm

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

I think mine is a little wider but not by much.
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Post by Wobbley 3/31/2024, 2:52 pm

The image from Norman is good but I’m not sure it’s optimal.  Eons ago when the high power targets had their black areas enlarged a lot of shooters went back to the issue sights that were larger than the “National Match” 0.062 width.  The reason was that the rifle shooters found that the post should be just a bit larger in width than the black.  Shooters found that the groups were “rounder” and smaller because there was less “shooter windage”.  The eye doesn’t see the whole image as shown and the brain tends to focus on the edge of the sight and the black.  If the post is drifting and the, say, left edge of the post is to the right of the black you’re no longer centered.  My technique was a “center of mass” hold so I didn’t care that much.  

As for notch width, I believe the ISSF pistol shooters start the refinement process with notches about 1.5 times as wide as the post and the post maybe 1.1 times as the black… so on a 25 yard center, the perceived width of the post would be 5.7 inches and the notch would be about 8.5.  They do enough holding training to imbed the image of the notch opening “centered” so the “light” on one side lets them know when the sights are centered.  Since the harder target is 50 yard, that perceived width would be 9 inches at 50 and 4.5 or 4.6 at 25 which is close to what you have.  So just be aware of the differences in the targets visually.k
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