Which iris and apertures sizes for 660/690 mm barrel?

nester · Post by **nester** » Wed Mar 07, 2012 9:25 pm

Which front iris and rear apertures are usually used for 50m with standard barrel?

I am using Anschutz Match 54 rifle with 660mm barrel and trying to find the proper combination. (Planning to order 1913 with 690mm barrel)
I used to like the small and narrow front sight - using Centra High End Crystal inserts 3.2/1.0 and 3.4/1.0, but I've noticed that during the match as fatigue increases and/or at the evening I have problems with getting clear picture, especially with 3.2 - the ring kind of "melts" and tend to disappear..
So now I have found myself increasing the iris size, and ring size as well.

So is this true that small and narrow inserts work mostly for very sharp and fresh eyes? But after 100 shots at 8pm you could barely see it - as it blurs completely?..

I am thinking about Centra variable iris - e.g. 2.8-3.8 with the ring width 1.2. (I still don't like thick 1.6 or 2.0)
Also, do colored glass (they can be blue, yellow, red) or rear filter would help?

About the rear aperture - I also like the small one (it helps me to easily center front sight in it) - I have 0.9-1.6 variable aperture and I use 1.1 to 1.2 all of the time. My current eye relief is extra long - about 8 cm/ 3 inch (due to long stock, and sight cannot be moved back).
With air rifle when eye is almost touching the sight (~1cm) I decreased it to 0.9 but it still seems too large for me.

I am thinking about Centra Sight 1.8 Competition or Centra Sight 3.0 Combi -
first one is 0.8-1.8, with 10 colors filter and polarizer, and second is 0.5-3.5 with 5 colors and polarizer.
So which are the usual sizes for the rear aperture with normal (1-2 cm) eye relief? Should I get as little as 0.5 mm, or it's better to get 10 color filter?

Here I've tried to make a photo - this is 3.6/1.0mm insert on the slightly bigger than normal SCATT target.
I'd say it is looks fine for the camera, but for the eyes insert looks slightly smaller and narrower, and after some time ring starts to blur..

justadude · Post by **justadude** » Thu Mar 08, 2012 11:48 am

It sounds like you need to look into shooting glasses.

You have not mentioned if you are shooting Prone or 3P and I assume at 50m. For a standard length barrel 3.2 is not a bad spot for 50m prone, in the upper positions, especially standing you will likely want larger. The rule of thumb is the aperture should appear at least 1.5X larger than the bull and also the bull should remain inside the aperture 100% of the time during the best part of your hold.

Unless you are on an exceptionally bright range your rear iris is too tight. Try this look through the sights, open the iris until things start to get fuzzy, then tighten down just a hair but not so far the image started to dim.

Eye relief mostly controls field of view, not aperture, so don't be afraid to go with 1.3 or so. Eric U has discussions about shooting with much larger rear irises than that.

Now, the human eye is not designed to focus on a front sight some 0.8m away. Sure, young eyes, fresh eyes in good light can do it but it is not natural. As you seem to find the front sight melting as the day wears on and presumably the light dims that might be a sign you could help things with vision correction and a set of the adjustable shooting frames.

Good Luck
'Dude

nester · Post by **nester** » Fri Mar 09, 2012 11:26 am

Generally - what are the methods to combat the eye fatigue?

Generally I do not have any complains about my vision, despite I work with computer (I am 35 years old), and in the morning/midday when I start shooting - I am perfectly happy with my sight picture and like the small and narrow insert, but after 30-40 shots (or at the evening) sight picture becomes the major problem - I have to blink to clear the picture, take some rest with eye closed and then really work to get the iris in focus, etc..

Is this a common issue (like numb left arm), or I need to change something in training (e.g. do not aim longer than 5 seconds, etc?), check the light conditions, or try colored filters/etc, or glasses?..

justadude · Post by **justadude** » Fri Mar 09, 2012 6:11 pm

Generally - what are the methods to combat the eye fatigue?

Things like don't just sit there and stare down the sights for an eternity before releasing the shot. Glancing around, looking down range between shots. Try not to look at things that are very bright. Don't have a front aperture that is so tight on the bull that you are looking for just the tiniest sliver of light. Open the rear iris a bit so things are bright and clear without being to the point of fuzzy.

Generally I do not have any complains about my vision, despite I work with computer (I am 35 years old), and in the morning/midday when I start shooting - I am perfectly happy with my sight picture and like the small and narrow insert, but after 30-40 shots (or at the evening) sight picture becomes the major problem - I have to blink to clear the picture, take some rest with eye closed and then really work to get the iris in focus, etc..

First, I am going to bet that you are far sighted. (When completely relaxed your eyes focus out past infinity.) At your age, you can still compensate and for most things, your eyes are fine but when it come to repeatedly trying to focus on something small about .8 meters away over time your eye gets tired of trying to focus at that distance. You might try just looking through the sights with some dimestore readers set for +.25 or +.5 diopters. While I am sure you figure your front sight is in focus you might in store for a treat in front sight clarity. If that is the case, then you can start to look at some made for the purpose shooting glasses.

Also, as I mentioned your iris settings are too small. Want a small field of view, move the rear sight forward, but let some light through. As for a rear iris, I shoot a Centra 1.8 Twin, mostly I use the grey filters for when the sun is bright on the face of the target. Occasionally in weird lighting I will dial in the colors to try to improve contrast.

Some folks get all worked up about the refinement in sight adjustment a tube gives you. Biggest thing a tube gives you is it sets the front sight out a few inches further, which also reduces the strain on the eyeball. I have had good luck with the "uptatuner". Helps both my eye and the barrel. Gotta be willing to put the time in to tune it though.

Is this a common issue (like numb left arm), or I need to change something in training (e.g. do not aim longer than 5 seconds, etc?), check the light conditions, or try colored filters/etc, or glasses?..

I really don't know how common this problem is. I know your approach of cranking down on the iris is not uncommon, all that does is reduce light to the retina in the eye, causing the iris to open out even more then making it even harder for the eye to focus.

Good Luck
'Dude

Tim S · Post by **Tim S** » Sat Mar 10, 2012 5:39 am

Personally I think 3.6mm is on the small side for prone. I'm well aware that (much) better shooters than me use small front apertures,. I think Eric U admitted to using a 4.3 (23in barrel and 12in tube). Personally I use the equivalent of a 4.0-4.1 (actually 4.8 with a short tube).

As for the actual insert, why not just use antother hi-end? An iris is nice, but is it worth the extra money? I.e will you use the full adjustment range, or just +/- 0.1/0.2. If you don't change the aperture much, individual inserts are cheaper.

I'm not surprised the foresight is blurring at 8pm after 100 shots, especially on an indoor range! You will be tired after working, tired after shooting, and indoor ranges are often too dim.

'Dude is right, close your eyes between shots, scope with your left. I'd also suggest drinking plenty of fluids through the day.

Tim

Vincent · Post by **Vincent** » Sat Mar 10, 2012 11:49 am

I was reading through the MEC Air Rifle book while figuring out if I needed to get a pair of shooting glasses. The book states that one reason for blurred vision could be the body's need for fresh oxygen and that one of the first things to go could be vision. I had a similar problem at a match where about 3/4's through the match I noticed my vision getting blurred. I still bought the glasses with a mild prescription and I recently set them up, but need to practice with them to see if they'll be effective for dealing with improving my vision.
I tried a Centra 1.8, but found that I prefer to keep the sight further back for more light. So I have the stock aperture in place and don't use an iris now. I do use an AHG 4.0 yellow front aperture for better contrast. It seems to help. I also have an AHG 4.1 pink aperture. The color is very mild but helps.