Aperture size for Mod Iron rifle?

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  • Last Post 07 July 2015
RicinYakima posted this 06 November 2014

I have one of those adjustable rear apertures for a new Mod Iron rifle I am trying out. Yesterday under grey skies, I was surprised how much better the groups were with it wide open. Is there some sort of “rule of thumb” for opening size; how much you can see of the front sight? I have used a small opening in the rear before, but that experience has me doubting my past usage. Ric

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gnoahhh posted this 06 November 2014

I think it is driven by the individual eyeball's need for clarity under a given light situation. (How's that for a politician-like response?!) In other words- whatever works best for you in any given situation. My rule of thumb is to use as small an aperture that best allows for clarity of front sight and target. Sometimes that means a pretty big aperture, sometimes not.

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R. Dupraz posted this 06 November 2014

I use an adjustable Merit eye disk on a Marlin 38-55 for lever action silhouette, only because it allows me to see the front sight at all anymore. And having shot NRA HP and long range BPCR with Aperture sights, I know of no rule of thumb for aperture size.   I think that it is a personal thing as the eyes “mature”   All the information Regarding aperture size that I know of back then, including seminars and such taught by champion shooters/instructers said , that small aperture size did not equate to small groups. Just the opposite. Contrary to my conventional thinking.      I also think that there is something else in play and directly related and that is the ability of the aperture, what ever size it may be, to make that front sight clear and sharp. Which of course tends to make smaller groups. I have used large apertures and have even taken the aperture out of the rear sight and shot small groups back when I could still see.      So, I tend to think that whatever size aperture it takes to make that front sight clear and sharp at the time is the right one. Actually I try for the largest size that I can.      My experience has born this out over the years.      

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onondaga posted this 06 November 2014

http://castbulletassoc.org/view_user.php?id=50>RicinYakima

A simple principle of optical depth of field applies to aperture size selection.  The smaller the aperture is, the more depth of focus is seen. The larger the aperture is in dim conditions the more light will be allowed through for view but depth of focus decreases as aperture size increases. This makes it advantageous to the shooter to use the smallest aperture size that can be used for the light conditions at hand. There is no universal size that works best all the time. Recognizing when you need to change aperture size is the key to getting the most out of an adjustable aperture.

Gary

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Ed Harris posted this 06 November 2014

The optmum aperture size approximates the eye pupil opening for the light conditions. A fully dialated eye in dark-adapted conditions is about 7mm, hence the miltary ghost ring for evenin nautical twilight. In bright sun it is about 1.5mm, hence the .062 aperture on the NM M1 rifle.

73 de KE4SKY In Home Mix We Trust From the Home of Ed's Red in "Almost Heaven" West Virginia

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RicinYakima posted this 06 November 2014

Gentlemen,

Thank you all very much, each added a piece to the answer. Yesterday the Merit would not open up enough, and I used one that I had drilled to 13.64ths.

Ric

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Tom Acheson posted this 06 November 2014

Standing behind a gun show table a few years back, I mentioned to a shooting friend that I had a new Model 74 Sharps and was having difficulty determining how to adjust the rear sight aperature. His suggestion.....people tend to use too small of an opening. The black bull you are shooting at should consume about 1/3 the area of the aperature diameter. 

So the dimension of the space between the edge of the bull and the inside edge of the aperature should be the same as the width of the bull. I tried it out and think he is on to something.

FWIW

Tom

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R. Dupraz posted this 07 November 2014

"Standing behind a gun show table a few years back, I mentioned to a shooting friend that I had a new Model 74 Sharps and was having difficulty determining how to adjust the rear sight aperature. His suggestion.....people tend to use too small of an opening. The black bull you are shooting at should consume about 1/3 the area of the aperature diameter."   Tom:   I was told the same thing back when I was shooting HP and was what I was alluding to when I wrote my reply but couldn't remember the details. But of course that was back when the front sight was clear and in focus.

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Pentz posted this 07 November 2014

Lucky guys...all I see through an aperture (and my spotting scope) is a cataract. Gonna have to dig into my gun fund and get it taken out soon.

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delmarskid1 posted this 07 November 2014

Some days I need to unscrew the damned thing and look through the threaded hole.

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Bud Hyett posted this 07 November 2014

Living in the mature age group where eyesight is initially fuzzier and slower in responding for focus, the larger aperture is a boon. My rule of thumb for a starting point is to have at least as much white around the target as the black dot is seen to be. When the day is bright, a person can first try and then possibly use a smaller aperture. Of course, in the Pacific Northwest, there are seldom that many bright days. There is also the consideration of your body responding to movement and a smaller aperture leading to excessive response and over-control. When first shooting Bullseye, I tried to hold as tight as possible on the bottom of the black and would over-control the gun, jerking shots out in the seven and eight ring. Once I learned to relax, and hold more white at 6:00 o'clock, the shots came easier with better scores. I've carried that lesson into rifle shooting, relax and see plenty of white. 

Farm boy from Illinois, living in the magical Pacific Northwest

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Brodie posted this 07 November 2014

Back in my 20's (before my eyes caught arm shortening disorder< can't get the print far enough away from the eye to be in focus> ) I was shooting an old Mod 70 Win 30/06 with a Lyman 48 and one of the adjustable apertures.  I shot several groups off the bench with the smallest aperture I could see through well , and with the aperture removed.  There was no attempt to quantify the data other than looking at the targets side by side.  I could find NO SIGNIFICANT DIFFERENCE in group size.  If anything the aperture less groups were a tad smaller.  My test was not scientific nor extensive, but it was enough to show me that I shot as well or better with a ghost ring than a pin hole.  Maybe if we have an optician or opthamologist in the CBA we can get a meaningful explanation.  Personally I don't need one. Brodie

B.E.Brickey

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R. Dupraz posted this 07 November 2014

My “rule of thumb” is and has been -- Listen to what that dang target is trying to tell me, then, go from there. The kiss principle rules.   The problem with that is though that often the circuit from the paper to the trigger finger gets shorted out along the way somewhere.

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Wineman posted this 08 November 2014

I went to a 0.052” custom aperture for my M1 Garand. I also use a +0.50 diopter increase to my normal distance prescription in my shooting glasses. In the sun it works great. I switched ranges and the new place has a covered firing line. My crisp front post went to a fuzzy stick and sharp bull instead of the opposite. With the shade my pupil is wider and more light through the sight would probably help.

Dave

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R. Dupraz posted this 08 November 2014

Welcome to the ranks.    (':D', 

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6mmintl posted this 02 July 2015

General rule of thumb is, close down aperature, then open slowly till light/view gets brighter, when you get a burst of light that is the optimal light/condition coming into your eye for best viewing.

Light constantly changes with/without clouds/haze/moisture/smoke and you may have to do this process more then once as the day wears on.

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Wineman posted this 07 July 2015

I added a 0.047 aperture sight to my M1 Garand thinking it would really make a big difference. Well it did, shot my worst CMP score “ever". At a covered range, it is really hard to see the front post. Even in bright sun, I did better with the stock sight.

Dave

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