rear sight aperture diameter?

[RickB]

Is there any rule of thumb concerning optimum aperture diameter as it relates to accuracy?
I was shooting both my Garand and AR on Saturday, and just could not get the AR to group.
Later (of course), I thought that the rear aperture on the M1 was smaller than the large aperture on the AR, and could I have improved my 100yd groups by switching to the smaller aperture on the AR?
What's the tipping point (distance) for using the smaller aperture?

 

[Mk VII]

Depends on the ambient light level and the age of your eyes.
Ageing eyes can find that a smaller aperture helps the definition - but if the light level is poor, as it may be at this time of year, then you may find it is not passing all the light the eye can use.

 

[JimPage]

For hunting in the woods, I usually take the aperture disc out of the sight and use just the holder part of the sight. So the answer is: "It all depends..."

 

[4EVERM-14]

Not sure which model rifles you shot.
The rear sight on a Rack M1 was about .100" diameter. The National Match sights were either .0595" or .0520".
The Ar battle aperture on the flip sight is about .187". Match apertures can be anywhere from.038" to .054".
To answer your question the smaller aperture will allow more depth of field giving better target reference. The down side is that lower light conditions make the picture very dark and difficult to hold.

 

[T. O'Heir]

"...aperture diameter as it relates to accuracy..." No. An NM aperture is/was .0595" or .052"(there's a .047" one too). Putting either on a rifle that doesn't shoot well will have no effect on accuracy any more than a telescopic sight will. The smaller aperture has to do with focus and increasing your depth of field. A NM rear aperture also has half minute adjustment.

 

[Slamfire]

Is there any rule of thumb concerning optimum aperture diameter as it relates to accuracy?

The only rule of thumb I can possibly think of is post sharpness. You want the post to have sharp edges. I trade off target clarity for post clarity. I wish I could both clearly, and there was a time I could, but now, I can't. So I am willing to trade off target sharpness for post sharpness.

Your eyes differ from my eyes. Your pupil diameter is different from mine. Guys whose pupils can shrink down to a pin point love bright days. Shooters with large pupils like over cast days. Since eyes are different, the aperture that works best for you will be different.

Too small a rear aperture and the target and post goes dark, so that is an obvious indication of a problem. I now have problems with the old 0.0520 and 0.0595" rear sight apertures of the M1a and Garand. I had my NM sight drilled out and I use an AR15 aperture. I use a 0.046" standing and a 0.042" all other positions. I use that same combination in my NM AR15's. I have buds who can go down to 0.036" which is too small for my eyes.

I was shooting both my Garand and AR on Saturday, and just could not get the AR to group.

An AR15 is like a snubbie. Short little sight radius. This is something that is absolutely critical to learn with an AR15: sight alignment is more important than sight picture. I was taught this by a Marine Shooter at Camp Perry. I was struggling with the occasional wild shot and assumed that I was putting the post in the middle of my sight picture, target in the middle, and I was not. At least not always. There is an old saw, that the military used to say, that the eye naturally centers the front sight if you are using a rear aperture. This is hogwash. You have to check your sight alignment each and every shot. Alignment is critical for all rifles, but you start using an AR15, a sloppy sight picture gets magnified.

Also, stock weld on a AR15 is different. Let the charging handle touch your nose and always line up on the gun with the charging handle at the same place on your nose. I could not do that standing, but since I always put the rifle in the same spot on my shoulder, my head would go down on the same stock spot each time. But prone or sitting, use that charging handle to locate your face.

 

[wogpotter]

Various adjustable & dial-in apertures used to be very popular. Some of the smaller ones were truly tiny & could only be use in the brightest light.
The fact of the matter is your eye & brain will "automatically" center the iris opening (aperture) behind any matching aperture. The trick is to match your iris opening to the diameter of the sights opening for minimum offset. Unfortunately its more theory than anything because your eye is constantly adjusting anyway & if you put an closed down (very bright light adapted) iris behind a tiny sight aperture guess what?
Yep, it opens up.

 

[RickB]

So, under the prevailing light conditions, seeing the sights through my eyes, I could see the sights/target better through the Garand's .10" aperture than through the AR's .187" aperture.
An aperture half the size of the Garand's may or may not have offered an improvement.
The lighting wasn't great, outdoor range with heavy baffles over and around the firing line and the sun fairly low in the sky, so maybe the smaller AR aperture would be really great in the Summer, but too dark in January.
Oh, well, it looks like I'll have to go to the range again!

 

[Jimro]

I once saw a optics guy analyze M16 sights with a ray trace to prove they were parallax free if you put the front sight post "generally in the middle" of the aperture. I consulted another guy to double check his work and he said it looked legit. I think this is where the myth of "just put the front sight post on the target and pull the trigger, you're eye will naturally center" comes from.

However the experience of all the M16 shooters and AR-15 High Power competitors I've ever known make that "parallax free iron sight" a complete lie. Of course I can't mathematically prove it, but then again the mathematical proof once said the bumblebee cannot fly.

So, I use a 0.052" rear aperture and a standard front site post. I use a 6 o'clock hold. A guy I used to work with used the same rear aperture size, but use a .073" width front sight post which to the shooter is wider than the aiming black of the targets. He said it let him focus on the front sight post better.

Anything smaller than a 0.052" is going to be very dim. But, if you have decent marksmanship even a milspec rear site is going to be fine, the point is to have the front sight in the center of the aperture.

Jimro

 

[wogpotter]

Of course I can't mathematically prove it, but then again the mathematical proof once said the bumblebee cannot fly.

Wild thought, lasers.
Bench mount a rifle, shine a tight beam laser through the rear sight just touching the tip of the front sight & see how much "wiggle room" there is at the target as the laser is tracked round the circumference of the peep aperture.
Might be an interesting experiment.