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Old October 27, 2008, 12:43 PM   #1
whiplash
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what does sight radius do for me?

I have read about having a good sight radius/picture. But I have never done any research about it. I have heard about the XD 5in tac having a better sight radius, over my XD 4in service. Can someone explain to me how that works? good/bad? just wondering...
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Old October 27, 2008, 01:09 PM   #2
Brian Pfleuger
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The further apart the sights are the better you are able to see misalignment and movement.

It can be said much more technically than that and with lengthy explanations of geometry but that's why it matters.
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Old October 27, 2008, 01:24 PM   #3
whiplash
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thanks for the quick reply. gotta like simple answers, thanks.
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Old October 27, 2008, 03:50 PM   #4
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Yes, longer distance between front and rear sights allows more precise alignment but if distance is too long, other negative factors can apply. Wobble increases as sight radius increases for one example. When shooting Bullseye competition, I shot S&W M41 pistol with 4", 5", and 7.5" barrels. My scores were higher with the 5" barrel. Later I tested S&W revolvers with barrels from 4" to 8 3/8" and found that I shoot best with barrels of 5"-6.5". I scored lower with shorter barrels (4") due to less exact aiming with shorter sight radius, and with longer barrels (7.5", 8 3/8") due to sight wobble and barrel droop. For me, either too short or too long sight radius will generate lower scores.
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Old October 27, 2008, 04:30 PM   #5
BillCA
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Sight radius is the distance between the rear sight and front sight. The greater this distance, the easier it is to get a precise alignment of the sights. Of course a longer radius usually goes hand in hand with a longer barrel which can increase fatigue and make your arms unsteady too.

The longer barrel, essentially, gives you more precision because the further the front sight is from the rear, the smaller the fraction of a degree it moves per 1/10th inch of your input. Conversely, the shorter sight radius gun's has a gross scale of motion for every 1/10th inch. If in a 6" gun, that 1/10th inch movement translates to an offset of 1/2" at 25 yards, that same movement will translate to a larger offset from a short barreled gun - perhaps as much as 1-1/2 to 2".

You are moving the barrel thru an arc to align the sights. If you think of a Sextant or protractor with a 12" radius, the markings per degree are spaced further apart. This makes precision alignment easier by allowing you to read fractions of a degree (minutes). But if that Sextant or protractor has only a 2-inch radius, the degrees are crammed together and provide less precision.

Clear as mud?
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Old October 27, 2008, 06:45 PM   #6
Brian Pfleuger
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Quote:
Originally Posted by BillCA
Sight radius is the distance between the rear sight and front sight. The greater this distance,...
Quote:
Originally Posted by Peetzakilla
It can be said much more technically than that and with lengthy explanations of geometry but that's why it matters.

See, I told you.
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Old October 27, 2008, 07:09 PM   #7
Japle
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It’s easy to hit a point of diminishing returns.

With a long sight radius, you can see tiny misalignments better. You try to correct them. While you’re doing that, your eyes start to get fuzzy because they’re the first organs to react to a lowering of blood oxygen. (You’re holding your breath, of course). Now it’s harder to see the sights. You start to shake slightly as your arms and hands get tired.
The smart thing to do is to lower the gun and get your breath back. But most people just want to get the shot off. They yank the trigger. The result is a poor group.

With a shorter sight radius, you can’t see the misalignments as well, but that’s OK. The misalignments aren’t really enough to screw up your group. The sights look good, so you shoot faster. You don't get short of breath. You can see the sights better. Your groups are just fine.

The exception to this is in hunting or metallic silhouette competition. You can shoot from a much steadier position. You can get everything aligned before you go into your final prep (breath, heartbeat) before the shot.

The pistol I used to use for the standing position is silhouette had a long sight radius. It also had a 6 oz trigger pull. The first time the sights looked right, I could get the gun to fire immediately. Can’t do that with a combat gun.
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Old October 27, 2008, 08:01 PM   #8
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The other aspect is that a longer sight radius usually means a longer gun and vice versa. Where this is relevant is that a 1/64th" misalignment on a short sight radius gun creates a larger error down range than the same 1/64" misalignment on a longer sight radius gun.
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Old October 27, 2008, 09:45 PM   #9
vox rationis
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Also the longer the sight radius, the less blurry the target will look as you are focusing on the front sight; if the sight radius is ultra short, the focus on the front sight will make your vision so, well I guess you can say myopic, or nearsighted, that it can get to the point where the target is so blurry that you can't see it anymore.
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