Front sight rear sight ration?

[Thedrifter]

Simply put I have recently created my own carbon fiber bloop tube “with limited resources” and am curious to know the ratio and how it works.

Here is what I have to deal with:
Factory FWB 2602 with Anschutz 7020 sight set, 26” barrel 22mm dia.
With the factory tube sighted in I have a well centered zero on my rear sight. I plan to keep this tube around in case of an unexpected failure.
When I switch to the new tube my Rear sight zero needed to be moved up 100 clicks placing it where you see it now:



This will not be enough to go to my 100 yard zero so I either need to raise my rear site about 4mm or (.2” inches) or trim some fat under my CF front sight.

From the best that I can figure the front sight height on the carbon fiber tube is sitting at 2.126” center of bore to center of sight. Sight length (front sight to rear sight distance) is 42.5”







The FWB tube front sight is sitting at 2.026” sight length is 34.5”

A difference of .1” is what I think I need to remove from the aluminum mounting block on the CF tube.
this would make swaping tubes easier and i wont have to worry about a drastic change in my zero when making a switch, if i ever have to.

Thoughts?

[KennyB]

It looks like you have an 8mm and a 4mm block under the foresight when using the FWB tube.

What I would do is:

use the 4mm block on the carbon tube rather than the 8mm block. That should drop the sightline and bring the rearsight back into the middle of it's elevation range.

Keep the 8mm block on the FWB and if you need to switch back, all you do is transfer the foresight and 4mm block as one item.

Otherwise you will need a 4mm shim under the rearsight - which is pretty normal.

Nice tube BTW.

K.

[Thedrifter]

It looks like you have an 8mm and a 4mm block under the foresight when using the FWB tube.

What I would do is:

use the 4mm block on the carbon tube rather than the 8mm block. That should drop the sightline and bring the rearsight back into the middle of it's elevation range.

Keep the 8mm block on the FWB and if you need to switch back, all you do is transfer the foresight and 4mm block as one item.

Otherwise you will need a 4mm shim under the rearsight - which is pretty normal.

Nice tube BTW.

K.

silver one has to stay, it is an offset riser. i have a 4mm riser i can add to the rear if it comes to that; however my sight are tall enough as is. I am more curious to know if turning my aluminum block down .1" is the correct math.

thank you for your reply though

[Tim S]

About .1in should do it I think. I've just measured the offset of my Nesom flipover 50/100 foresight, and the difference is 2mm, which is a shade under 0.1in.

Here's another idea though. Why not make a second foresight mount on the collar, directly oppoiste the first, and 0.1in lower. Rather than fiddle about cranking the rearsight (and cheekpiece), just loosen the collar, turn through 180 degrees, and put the foresight there. No more losing count of how many clicks you added!

[gwsb]

No reason to reinvent the wheel. Wouldn't a two step base work?

[KennyB]

By my reckoning 0.1" should give you roughly 8.5" more elevation at 100 yds.
Here's my attempt at the maths.

42.5" sightbase = 1.18 yards.
If the rearsight is 100.3 yards from the target ( i.e a foot back from the line) then the ratio of "rearsight to foresight" : "rearsight the target" is

1.18 : 100.3 = 1 : 85

so a 0.1" decrease in foresight height will result in a 8.5" higher POI

If it were me, I'd want a bit more than that as your rise from 50 to 100 will have increased by the ratio of your old sightbase to your new sightbase.
If your old sightbase was 32" and your new sightbase is 42.5" then 80 clicks of come-up becomes 106 clicks.

K.

[Thedrifter]

By my reckoning 0.1" should give you roughly 8.5" more elevation at 100 yds.
Here's my attempt at the maths.

42.5" sightbase = 1.18 yards.
If the rearsight is 100.3 yards from the target ( i.e a foot back from the line) then the ratio of "rearsight to foresight" : "rearsight the target" is

1.18 : 100.3 = 1 : 85

so a 0.1" decrease in foresight height will result in a 8.5" higher POI

If it were me, I'd want a bit more than that as your rise from 50 to 100 will have increased by the ratio of your old sightbase to your new sightbase.
If your old sightbase was 32" and your new sightbase is 42.5" then 80 clicks of come-up becomes 106 clicks.

K.

Thank you, this is what i was looking for,

and yes it does become 100clicks, I have an Uptagrafft tuner tube that i have been using the last couple months (Same length) but i found it to be too heavy.

Thanks for the help guys, sounds like .15" might be more usefull to shave off the front.