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Reuced rear aperture for improved accuracy

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ShootingSight View Drop Down
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    Posted: Jun 13 2020 at 3:39pm
I have been making reduced rear apertures for the M1, for use in the Garand match, and they have been very successful.  This is done by simply replacing the rear aperture with one I have silver soldered a reducer shim on.  I got CMP approval that these could be used in the 'as issued' category.

I never went there with the Carbine, even though the shorter barrel length means a shooter would benefit even more from a reduced aperture.  Reason was there was no easy way to replace a part on the rear sight - they were not meant to be taken apart.

Recently, after years of mulling it over, I finally have a solution, and I got CMP blessing that they were legal.  I actually have 3 options:

1.  A plastic tubing insert that you can thread in to the sight, then trim flush.  It compresses going in, so I'm not sure it needs adhesive, though maybe it does not hurt.  Advantage is you do not alter your carbine if it is collectable.  Disadvantage: it took me a long time to find a commercial source of the correct diameter tubing, and it is only available in one size - it is advertised as 0.044, though after compression, I need to re-check.
2.  I sized up a tap and set screws, so you can run a tap into the rear sight, then I made a collet so I can drill set screws, and you can screw in an aperture insert.  Advantage is I can drill the set screws in different sizes, disadvantage is that you need to cut threads in the sight, which a collector might not want to do.  Good news is the threads do not enlarge the opening, so if you take out the set screw, and dab it with black paint, you will never see it, unless you are looking for it.
3.  I found a source of commercial rear sights, which I can execute #2 option on.  You don't need to modify a USGI sight, though you do ruin the two stages that hold the sight in place.

Clearly not for everyone, but if you shoot at Perry, I guarantee this will add 10 points to your score.

Art

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Post Options Post Options   Thanks (3) Thanks(3)   Quote jackp1028 Quote  Post ReplyReply Direct Link To This Post Posted: Jun 13 2020 at 9:47pm
I've done the same thing using the red tube that comes on the spray nozzle of aerosol cleaning products such as WD-30. Just poke it through the aperture and cut it off with a razor blade. It's a slight press fit and not likely to fall out. It leaves an aperture of about .040".





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Post Options Post Options   Thanks (0) Thanks(0)   Quote Charles Quote  Post ReplyReply Direct Link To This Post Posted: Jun 14 2020 at 8:38am
Another possibility for a non collector would be to carefully fill the hole with  J B Weld, let dry and drill a hole of the desired size.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Donnie Quote  Post ReplyReply Direct Link To This Post Posted: Jun 14 2020 at 2:54pm
Such clever solutions! Clap

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Post Options Post Options   Thanks (0) Thanks(0)   Quote W5USMC Quote  Post ReplyReply Direct Link To This Post Posted: Jun 14 2020 at 4:36pm
Never gave much thought to reducing the size of the aperture until I read this thread. I decided I had to try it for myself to see if it really made a difference. I went with Jackp's suggestion since that is what I had on hand, Holy Sh@T what a great idea, tightened my group considerably. Thought that it would be harder to focus on the front sight tip through the smaller hole but it was the exact opposite. Thanks for posting this ShootingSight and JackP.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jackp1028 Quote  Post ReplyReply Direct Link To This Post Posted: Jun 14 2020 at 5:03pm
The small aperture on the rear sight does the same thing that a smaller F-stop does on a camera lens. It increases the depth of field (focal length) of the view and sharpens the image (target). Although the image may not be as bright, it will be sharper. A camera compensates for this by increasing the time that the shutter is open. It's particularly helpful for us old timers who have trouble adjusting our focus between the rifle's sights and the target. Younger shooters may not notice as much difference with a smaller aperture.

This is how Matthew Quigley was able to hold a 4" group at 600 yards with his 45/110 Sharps rifle.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Uncle Mike Quote  Post ReplyReply Direct Link To This Post Posted: Jun 14 2020 at 7:26pm
Hi, I like the idea of the plastic "straw". I will try it. I also like that it is not permanent and red, regards, Mike
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 03manV Quote  Post ReplyReply Direct Link To This Post Posted: Jun 14 2020 at 9:58pm
You may find that the red is not a benefit, the plastic is actually translucent.
When I tried it today, I found the red distracting and not at all "clear".
A bit of Black magic marker on both sides sharpened the sight picture considerably and allows the aperture to just blend into the rest of the sight.

Don
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Uncle Mike Quote  Post ReplyReply Direct Link To This Post Posted: Jun 15 2020 at 9:46am
Originally posted by 03manV 03manV wrote:

You may find that the red is not a benefit, the plastic is actually translucent.
When I tried it today, I found the red distracting and not at all "clear".
A bit of Black magic marker on both sides sharpened the sight picture considerably and allows the aperture to just blend into the rest of the sight.


Hi, that's interesting and I see more experimenting is called for, regards, Mike
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Post Options Post Options   Thanks (0) Thanks(0)   Quote W5USMC Quote  Post ReplyReply Direct Link To This Post Posted: Jun 15 2020 at 10:59am
Originally posted by 03manV 03manV wrote:

You may find that the red is not a benefit, the plastic is actually translucent.
When I tried it today, I found the red distracting and not at all "clear".

The red was fine for me, the only thing that should be "clear" with proper sight alignment and sight picture should be the tip of the front sight. 




Edited by W5USMC - Mar 15 2022 at 6:36pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Uncle Mike Quote  Post ReplyReply Direct Link To This Post Posted: Jun 15 2020 at 11:32am
Hi, I placed a Surefire flashlight on the end of my Carbine and with a little white paint on the front sight it lights it up very brite, YMMV, regards, Mike


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Post Options Post Options   Thanks (0) Thanks(0)   Quote blackfish Quote  Post ReplyReply Direct Link To This Post Posted: Jun 15 2020 at 1:27pm
Originally posted by W5USMC W5USMC wrote:

The red was fine for me, the only thing that should be "clear" with proper sight alignment and sight picture should be the tip of the front sight. 


With a pinhole (and good eyes), EVERYTHING is in focus, in particular, both front sight AND target. Try that using a normal sight.

So the smaller the hole the better the focus (depth of field approaches infinity). And the shorter the "straw", the more light gets thru to your retina, and ultimately your brain.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote 03manV Quote  Post ReplyReply Direct Link To This Post Posted: Jun 15 2020 at 3:19pm
Originally posted by W5USMC W5USMC wrote:

Originally posted by 03manV 03manV wrote:

You may find that the red is not a benefit, the plastic is actually translucent.
When I tried it today, I found the red distracting and not at all "clear".

The red was fine for me, the only thing that should be "clear" with proper sight alignment and sight picture should be the tip of the front sight. 


By "clear" I meant the aperture, the red being translucent allowed light to pass through and did not give a sharp aperture- but an ill defined red ring that was quite distracting to me.
But then your red "straw" may have been denser than the one I picked up.
I thought I had a black straw around, but could not find one.

The small aperture is definitely an improvement, but coloring it black give me a much sharper image of the front sight.

Your mileage may vary. ;)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ShootingSight Quote  Post ReplyReply Direct Link To This Post Posted: Jun 18 2020 at 11:50am
WTF?  Seriously?  I spent a couple of years looking for the correct size tubing, and all I had to do was pick one of the dozen cans of WD-40 that are sitting all around my shop?  Damn.  Talk about a solution at the end of your nose.  Well done spotting that.

So now I sell reduced apertures, and you get a free can of WD-40 with every purchase :-)

So here is how the optics work:

Your eye focuses at a point.  Normally, the relaxed human eye focuses at infinity (ie 20/20 vision).  You then use your ciliary muscle in the eye to deform the lens and bring your focus closer.  When you shoot, what your brain actually does to see the front sight and the target at the same time is that it will focus at the optical average of the two, called the hyperfocal distance in photography.  So the front sight is just a little blurry, because it is closer than the focal point, and the target is just a little blurry because it is beyond the focal point.  So everything is a little blurry, but the average blur in the sight picture is at a minimum.  If you were to shift your focal point closer, the sight would get sharper, but the target would get blurrier, and vise versa.

Enter aperture size.  Smaller apertures improve your eye's depth of field.  What is depth of field?  Well it is a measure if you take an object that is at your perfect focal point, and you start moving it away from that focal point, how fast does it get blurry.  Specifically, how far away can you go (both closer and further) until the amount of blur gets too big.  So, if you have a small aperture, and your eye is focused at the aforementioned hyperfocal distance, the amount of blur you see on the sight is driven by the aperture size.  Downside is that it lets in less light.

The sweet spot I have found from making Garand apertures is about 0.042"

Length of tube does not play a role.

Next: corrective lens: I told you you need to flex the ciliary muscle to pull your focus in close.  Unfortunately, at 43 years +/- about 3 years, some 70% of us will discover that the lens in your eye loses flexibility, and the muscle cannot flex it as far anymore.  You start holding menus further from your face, and you start buying reading glasses.  What reading glasses do is they add a lens in your eye's optical path that artificially shifts your eye's relaxed focus closer to you, so you do not need to get your eye muscle to do it, and you can read without straining your eye.

Same is true for shooting.  Your front sight is not as close as reading, but your eye muscle is still straining, and what you see is that after 5 or 6 shots in slow-prone, your eye muscle starts to fatigue, the front sight starts to fuzz and fade, and you start stringing your shot groups up/down.  Reading glasses are much too strong.  Even the weakest +1.25 will bring your focus too close.  You will see a razor sharp front sight, but the target will be too blurry.  Answer is you need weaker than 1.25.  I do not have the distance from your eye to the front sight on a Carbine memorized, otherwise I could do the optical math for you, so I'll post a follow up with the correct lens strength, but there is an optimal power that will let your eye focus at the desired hyperfocal distance while leaving the eye muscle relaxed, so you can stare at your sights all day long and they will not fade.

Bottom line, optimal sight picture is achieved by getting your eye to the hyperfocal focus through lens selection, and then building the maximum depth of field around that focal point through reduced aperture.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote blackfish Quote  Post ReplyReply Direct Link To This Post Posted: Jun 18 2020 at 1:21pm
Originally posted by ShootingSight ShootingSight wrote:

Length of tube does not play a role.


It certainly does. Just look at any early flip sight for carbine, even a repro. Why is the aperture dished like it is? It's to make the "tube" (the hole aka aperture) shorter.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote ShootingSight Quote  Post ReplyReply Direct Link To This Post Posted: Jun 18 2020 at 4:17pm
Sorry - let me clarify: Length of tube does not play a role in the optical properties of focus or light transmission.  However if you have a long tube, alignment of the tube with your line of sight suddenly becomes important.  If a long tube is slightly askew, the open area is the projected diagonal of your line of sight, which will reduce the effective cross section to something smaller than the tube ID.

So it is beneficial to have the shortest possible 'tube', though the reason is not because tube length influences focus or the amount of light that comes through.

One further note, I went and tried this.  It does not work with WD-40, as their tubes are about 0.110" in diameter, and the opening is 0.080.  However I found another spray can of cleaner tha has a 0.084 tube, and that one is a nice fit into the opening.
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Timothy Quote  Post ReplyReply Direct Link To This Post Posted: May 17 2022 at 9:23pm
Stumbled on this thread the other day and thought it might do the trick for my 64-yr old eyesight.
Nice tighter group for me at the range today thru the reduced peephole diameter. 
A WD-40 tube was too big for my type 2 Hemphill - but the tube from a Balistol can was perfect diameter for a slight press fit. 
Thanks for the posts.
T R
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Timothy Quote  Post ReplyReply Direct Link To This Post Posted: Jun 16 2023 at 11:18am
I continue to be satisfied with the red tube method for my carbine.
I tried to find the right size nozzle tube for my Garand and M1903A3 rifles but not successfully.
Has anyone tried the reduced apertures offered by shootingsight.com? They offer apertures for a variety of milsurp rifles. I note that the one for the carbine is similar to the DIY version the original poster suggested (requiring alteration of the USGI sight or use of a repro substitute) but the apertures for other rifles don't seem to require altering original parts.

 If someone has purchased a sight from them, any comments on the quality of their sights whether for the carbine, garand or other rifle?

T R
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Marty Black Quote  Post ReplyReply Direct Link To This Post Posted: Jun 16 2023 at 11:46am
I tried ShootingSight's "red tube" idea on my "competition carbine" 3 years ago when this thread started, and was very pleasantly surprised how it tightened my groups. I cut off the excess with a razor blade and blackened the red tube with a felt-tip marker. You have to look hard to see that it's there.

I also installed a drop-in "NM type" rear aperture on my competition Garand. I bought two different sizes before settling on the best one for me (as discussed above, the amount of light that is let in varies with the size of the aperture).

Also, I've got a "USMC type" (wider) front sight on my competition 03A3, and that made a WORLD of difference! With aging eyes (I'm 72 now), I could not get a tight focus on that GI-issue skinny front sight. Hell, I could barely see it! The USMC type makes the 03/03A3 sight picture look like the Garand.

I strongly recommend all 3 alterations to these rifles.

Regards, Marty Black
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Post Options Post Options   Thanks (1) Thanks(1)   Quote 03manV Quote  Post ReplyReply Direct Link To This Post Posted: Jun 16 2023 at 2:53pm
If the tube is too large in diameter, just use a little sandpaper to taper it.
You'll get the hang on it pretty quick, then you can press the tube into the sight and cut off either or both ends as necessary.

Darkening the tube does help most folks it seems from reading the posts.Geek
Don
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