determining front apeture size

[Ltdave]

ive heard all of the ideas people have for a tight clearance aperture and for having a large (1.5-2.0 x the size of the bullseye) but i got some partial information today on there being a scale (chart) that uses a measurement (front aperture to eye) and the size of the bullseye, which will give you a STARTING POINT for which size to use...

does anyone have this chart or something close? i think my daughter may be struggling with smallbore because of the aperture size she is using. she must have the right aperture for her air rifle because she shoots that quite well...

[Scott J]

Ltdave,
Here is something from USA Shooting. Maybe it will help.>>>http://www.usashooting.org/library/Inst ... b_2011.pdf
Hope this helps!


Scott

[Tim S]

I'll go out on a limb here, but for a standard length barrel (i.e. Anschutz 1907 or 1913 with no extension tube) 3.6mm
is my minimum starting point for the ISSF 50m target in Prone, irrespective of the actual sight radius. Standing and kneeling usually need a larger aperture size to compensate for the less stable hold.

Ring thickness is also a factor, at least for me; I find I need a slighter larger aperture with a thick-ringed iris than with a 1.4mm thick glass insert.

[Ltdave]

Ltdave,
Here is something from USA Shooting. Maybe it will help.>>>http://www.usashooting.org/library/Inst ... b_2011.pdf
Hope this helps!


Scott

this is what i was looking for...

thanks

[abinok]

Cropped for easy printing....

[Thedrifter]

I'll go out on a limb here, but for a standard length barrel (i.e. Anschutz 1907 or 1913 with no extension tube) 3.6mm
is my minimum starting point for the ISSF 50m target in Prone, irrespective of the actual sight radius. Standing and kneeling usually need a larger aperture size to compensate for the less stable hold.

Ring thickness is also a factor, at least for me; I find I need a slighter larger aperture with a thick-ringed iris than with a 1.4mm thick glass insert.

This is amusing to me, mostly because I found the same thing last weekend, Im in the process of switching rifles and I do not have a sight tube on the new one, Factory 69cm Anschutz. While in Position, I had my friend adjust the front aperture till I had the best sight picture on the bull, about 3-4 times each we started small and worked our way open till i told him to stop, then from large to small, I consistently chose the 3.6mm

[imac]

front sight element to eye distance in mm x the diameter of bull ÷ by the distance in mm

900 x 112 = 100800

100800 ÷ 50000 = 2.016mm this is the apparent size of the bull. front sight element would = 2 × 2.016 = 4.03mm

This will work for any target at any distance as long as you know the 3 measurements in metric millimeters

[mtncwru]

I'll go out on a limb here, but for a standard length barrel (i.e. Anschutz 1907 or 1913 with no extension tube) 3.6mm
is my minimum starting point for the ISSF 50m target in Prone, irrespective of the actual sight radius. Standing and kneeling usually need a larger aperture size to compensate for the less stable hold.

Ring thickness is also a factor, at least for me; I find I need a slighter larger aperture with a thick-ringed iris than with a 1.4mm thick glass insert.

This is amusing to me, mostly because I found the same thing last weekend, Im in the process of switching rifles and I do not have a sight tube on the new one, Factory 69cm Anschutz. While in Position, I had my friend adjust the front aperture till I had the best sight picture on the bull, about 3-4 times each we started small and worked our way open till i told him to stop, then from large to small, I consistently chose the 3.6mm

I'm the guy who was cranking Cameron's front aperture that day, and it was actually a really great experiment. I did it optometrist-style: started at the smallest setting, and increased by 0.4mm each time until he said his sight picture was worse than the previous setting. Then I worked backwards in 0.1mm increments until I passed the "that's better" threshold again. Each time I made sure to occlude his front sight with my hand so he couldn't see which way I was turning things, and each time I had him close/open his eyes or look away to get a true reading. Once I had a reading, we did the same thing from the other direction. Both times he settled on the same reading (3.6mm).

On the subject of ring thickness, I, too, have found that I prefer a slightly thicker ring. I recently replaced nearly all my shooting gear and opted for a 2.0mm-thick ring, as opposed to the standard 1.6mm standard. My sight radius is quite long (receiver plus 27" barrel plus 12" Upta tuner), for a grand total of right around 44" from front sight to eyeball. So far the thicker ring has proven much easier on my eye, since it keeps the proportions of black in my front sight picture all closer to equal. I can certainly see the value of an adjustable-thickness iris (in addition to adjustable diameter), depending on what all you use that front sight for.

[imac]

I'll go out on a limb here, but for a standard length barrel (i.e. Anschutz 1907 or 1913 with no extension tube) 3.6mm
is my minimum starting point for the ISSF 50m target in Prone, irrespective of the actual sight radius. Standing and kneeling usually need a larger aperture size to compensate for the less stable hold.

Ring thickness is also a factor, at least for me; I find I need a slighter larger aperture with a thick-ringed iris than with a 1.4mm thick glass insert.

This is amusing to me, mostly because I found the same thing last weekend, Im in the process of switching rifles and I do not have a sight tube on the new one, Factory 69cm Anschutz. While in Position, I had my friend adjust the front aperture till I had the best sight picture on the bull, about 3-4 times each we started small and worked our way open till i told him to stop, then from large to small, I consistently chose the 3.6mm

I'm the guy who was cranking Cameron's front aperture that day, and it was actually a really great experiment. I did it optometrist-style: started at the smallest setting, and increased by 0.4mm each time until he said his sight picture was worse than the previous setting. Then I worked backwards in 0.1mm increments until I passed the "that's better" threshold again. Each time I made sure to occlude his front sight with my hand so he couldn't see which way I was turning things, and each time I had him close/open his eyes or look away to get a true reading. Once I had a reading, we did the same thing from the other direction. Both times he settled on the same reading (3.6mm).

On the subject of ring thickness, I, too, have found that I prefer a slightly thicker ring. I recently replaced nearly all my shooting gear and opted for a 2.0mm-thick ring, as opposed to the standard 1.6mm standard. My sight radius is quite long (receiver plus 27" barrel plus 12" Upta tuner), for a grand total of right around 44" from front sight to eyeball. So far the thicker ring has proven much easier on my eye, since it keeps the proportions of black in my front sight picture all closer to equal. I can certainly see the value of an adjustable-thickness iris (in addition to adjustable diameter), depending on what all you use that front sight for.

So I'm going out on a limb here

ISSF 50m target I'll take an educated guess you're using a 5mm - 5.1mm front element?

[mtncwru]

So I'm going out on a limb here

ISSF 50m target I'll take an educated guess you're using a 5mm - 5.1mm front element?

Only about a 4.5, surprisingly. I've tried bigger, but I don't like it, as I start picking up the edge of the paper, at least in my head. On electronic targets I have no trouble with the smaller aperture since it's an extra large, bright white field.

[imac]

I don't have great vision, with correct glasses I see slightly better than 20/20 but struggle with a couple of very large floaters grrrrrrrrrrrr. I work on the aforementioned mentioned formula to get as close as possible to having a 2 target size front sight. You are running at 1.8 works for you.
I spent hours on mx02 scatt trying all sorts of front sight elements and 2 x was what gave me best aiming average of 105.4 . I've just got myself a nice new KK500 so it's back to the calculator and then test it out again! Love the scatt saves mega ammo for this type of testing.

[mtncwru]

Yeah, the fatter ring helps a lot, too. It just stays sharper, at least to my eyes.

Totally agree on the SCATT, too. As soon as the IRS check clears I'll have one, too!

[imac]

Yeah, the fatter ring helps a lot, too. It just stays sharper, at least to my eyes.

Totally agree on the SCATT, too. As soon as the IRS check clears I'll have one, too!

Excellent stuff. I shoot air rifle small bore and full bore dry and live fire. If you use it on full bore rifle run a layer of insulation tape round barrel or it may move a little under recoil.
Also when you shoot outdoor if it goes from cloudy to bright sun it can be a little painful as the contrast will change and you miss most of the trace being recorded. The preview screen is as the camera sees things so spend some time to get a decent contrast thing unclick the preview and fire activation shot.

A small issue with an otherwise fantastic tool.