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Old December 2, 2011, 12:04 PM   #1
bpeezer
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Minimum distance between iron sights

How close together can I possibly mount iron sights with them still being relatively accurate? By relatively accurate, I mean I would be ecstatic with 8-10 inch groupings at 100 yards.

I want to test out putting BUIS on a bolt action rifle and just seeing what happens. This is just for fun, I wouldn't be hunting with it or attempting to be accurate on paper or anything. I was wondering if it would be possible to mount iron sights on a standard scope rail. The distance between the sights would likely be 6-7 inches...is this feasible?

I realize that if I wanted to use iron sights I should mount the front sight further along the length of the barrel, but if it's possible (and safe) I would like to try putting both sights on the rail.
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Old December 2, 2011, 12:08 PM   #2
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Id say no less than pistol length, so about 6 inches. The main thing is you need the front post as far away as possible. you can actually shoot without the rear sight with pretty good accuracy at less than 100 yards. (by pretty good i mean capable of shooting a human sized target)
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Old December 2, 2011, 12:43 PM   #3
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I have seen them mounted on top of a scope.
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Old December 2, 2011, 12:54 PM   #4
bpeezer
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Since it appears to be a viable option, is there a certain type of sight that should be used for this purpose? Or could I just stick on any standard iron sights and plink away? I like the Magpul MBUS, and that's something that I could put on another rifle later on for more useful applications. Would they serve me well?
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Old December 2, 2011, 02:06 PM   #5
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You might want to look at your eye's ability to focus.
A gentleman who was teaching me how to build a muzzle loader showed me(with an OPEN sight) to put the front sight on with double stick tape.Then sighting over the barrel,slide the rear sight forward till the shooters eye can put the front/rear sight picture in focus.His belief was the quality of the sight picture trumped a few inches of sight radius.

I assume you are talking about a rear peep sight.Its fine for that to be very close to your eye,and no ability to focus on the rear peep is necessary.

The front sight is another matter.The front sight needs to be far enough from your eye to get a good focus on the front sight and at the same time,at least a good reference of where you are placing it on the target.Beware having your front sight too close to focus .
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Old December 2, 2011, 03:32 PM   #6
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What is your intended use? Backup in case the scope fails? If so, I would look at something that can mount to your scope base in back, and install an appropriate front sight on the rifle. You will never see it through the scope.
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Old December 2, 2011, 06:00 PM   #7
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No, my intended use is just for fun. I can't think of anything I would be doing that would cause a scope to fail, I just think it would be a lot of fun to shoot my rifle with some iron sights. I don't care too much about accuracy with the iron sights, as I'm not too accurate anyways
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Old March 11, 2014, 10:41 AM   #8
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Trivia question.

What is the distance between the front sight post and the rear sight aperture, along the axis of the barrel and the receiver, the line of sight, what is that distance called or referred to as?
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Old March 11, 2014, 12:41 PM   #9
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Sight radius.

It was originally standardized in the USA and Great Britian on rifles as 30 inches a century ago or more. Adjustable rear sights mounted on the back end of rifle receivers were made with lead screws having 40 tpi. One third turn move the aperture .00833 inch which is exactly 1/3600th of a 30-inch sight radius; most barrels were 24 inches long so the front sight was about an inch back from their muzzles. There's 3600 inches in 100 yards. The rest of this should be easy for most folks to figure out.
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Old March 11, 2014, 01:27 PM   #10
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As you get older, the eye's ability to focus on near objects gets more difficult. I have found that by switching to an aperture sight on rifles, I can more easily hit what I'm aiming at. With Patridge type sights, I end up with basically putting a blurry post in the middle of the blurry groove if the target is in focus. With an aperture site, I don't have to worry about the rear sight and just have to put the front sight on the target. My old eyes appreciate this.
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Old March 11, 2014, 01:45 PM   #11
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How close together can I possibly mount iron sights with them still being relatively accurate? By relatively accurate, I mean I would be ecstatic with 8-10 inch groupings at 100 yards.
Sights aren't accurate. A shooter is accurate. So the question becomes, how close can you mount the front and rear sight together and still shoot accurately?

I can't answer that, but I can give you some food for thought.

Assuming that the front sight is over the muzzle (or slightly behind as when found on a gas block) you can bet away with AK level accuracy with 14.9 inches, or M4 accuracy with 14.5 inches. With an M4 with iron sights, 4 minutes of precision is easily achieved.

An MP5 has a 13.2 inch sight radius, but it is a 7-8 MOA weapon mainly because of how the 9x19 functions through that weapon. Obviously if you were shooting a 9x19 at 100 yards this translates into 7-8 inches, still within your "ecstatic" level of accuracy.

An Olympic level pistol shooter will easily achieve 8-10 MOA accuracy, but that is with a pistol held at arms length away, bringing the rear sight into alignment with the eye, not having the rear sight up against the eye like a military style apeture.

Hope this helps.

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Old March 11, 2014, 02:03 PM   #12
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An Olympic level pistol shooter will easily achieve 8-10 MOA accuracy, but that is with a pistol held at arms length away, bringing the rear sight into alignment with the eye, not having the rear sight up against the eye like a military style apeture.
Sweet I should try out for the olympics I can shoot better than that.

Seriously A NRA B-6 50 yard target's 10 ring is right at 4 MOA and they shoot one handed off hand.
I've shot 6" to 8" groups at 100 with a 4" revolver moving sights closer just make margin of error smaller.
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Old March 11, 2014, 02:14 PM   #13
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http://en.wikipedia.org/wiki/25_metre_rapid_fire_pistol

Maybe you should. The 10 ring on the 25 meter target is 4 cm, which would be 16 cm at 100 meters, or roughly 6.3 MOA.

Would be nice to see more Americans take home medals for the shooting sports

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Old March 11, 2014, 02:36 PM   #14
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Maybe you should. The 10 ring on the 25 meter target is 4 cm, which would be 16 cm at 100 meters, or roughly 6.3 MOA.
That's rapid fire they have to get 5 shots off and only have the target exposed for 8, 6 or 4 seconds, OP didn't ask about minimum sight radius for rapid fire
I suppose you think cross country skiing while shooting off hand is a good representation of what an average guy can do off a benchrest.
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Old March 11, 2014, 05:06 PM   #15
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Single shot free pistols have sight radiuses up to 18 inches. The 50 meter target's 10 ring is about 2 inches. 9 ring is about 4, course of fire is. 60 shots. USA record is 574. A good friend, Don Hamilton (bless his departed soul) holds the civilian record of 569.
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Last edited by Bart B.; March 11, 2014 at 05:16 PM.
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Old March 11, 2014, 06:30 PM   #16
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That's rapid fire they have to get 5 shots off and only have the target exposed for 8, 6 or 4 seconds, OP didn't ask about minimum sight radius for rapid fire
I suppose you think cross country skiing while shooting off hand is a good representation of what an average guy can do off a benchrest.
No one cross country skis while shooting offhand. That would be unsafe. Biathletes generally skiing first.

The OP didn't ask about a lot of things, that he didn't ask about rapid fire has nothing to do with my answer other than combat oriented carbines and pistols have the shortest sight radius measurements of any common firearm.

But if you are as good of a shot as you say you are, by all means try out for the Olympics. Even if you don't make the team you'll still get a good story to tell.

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Old March 17, 2014, 01:22 PM   #17
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Quote:
Bart B. replied:

Sight radius.

It was originally standardized in the USA and Great Britian on rifles as 30 inches a century ago or more. Adjustable rear sights mounted on the back end of rifle receivers were made with lead screws having 40 tpi. One third turn move the aperture .00833 inch which is exactly 1/3600th of a 30-inch sight radius; most barrels were 24 inches long so the front sight was about an inch back from their muzzles. There's 3600 inches in 100 yards. The rest of this should be easy for most folks to figure out.
Yep, exactly. Well done! ... and a darn nice further explanation to boot.

All shooters should understand sight radius first and formost, and learn on iron sights verses glass IMHO. Too many kids are being broken-in on glass these days.
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Old March 17, 2014, 03:16 PM   #18
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HiBC You might want to look at your eye's ability to focus.
Yep, make sure that you can focus clearly on the front sight.
Positioning the front sight too close to older eyes is not a good idea
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Old March 17, 2014, 03:51 PM   #19
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To compliment my above post on sight radius, here's how the scopes started out over a century ago.

Their external adustments had a spacing of 7.2 inches. With the same tooling making the knob's threads also 40 tpi and the sprung ball detents making 50 clicks per revolution, each click moved the back mount's adjustment flats exactly .0005". With 1/3600th of 7.2 inches being .002", four of those clicks moved the scope 1 inch at 100 yards. Some scope bases were mounted 10.8 inches apart giving 6 clicks per inch at 100.
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