Making a fixed rear sight, can I calculate required sight height?

[flying pig]

I have an old Ross 1905-R sporter that has had a rough life and has been bubba'd a bit. I tried a receiver mounted target sight and it does not allow dropping the elevation screw low enough to be practical for the shooting I'll be using it for. This little rifle is very accurate and very light, and I love the platform. Therefore it's worth my effort. The plan is to build a base with an aperture sight fixed on it at the rear of the receiver. I have the sight alignment figured out, now I'll just have to measure its position. As for the elevation, can I calculate the height I need? I want it 3" high at 100m, with the aperture set to lowest setting on the target sight it is 12" high at 75m.

Thanks!

 

[hunter5425]

Here's something ht tps://www.youtube.com/watch?v=VbmARJu0Xho

 

[guntech]

You will want the front sight about 50 thou lower than the rear sight in relationship to the bore... that will get you started...

 

[B_noser]

Here is a method of doing a rough calculation. I think it should get you in the ballpark. You have given your desired and current poi at different ranges and one would need to know the difference at the same range - let's say 100 yards. For the sake of argument, let's say it is shooting 12" high at 100 yds and you want it to shoot 3" high. The desired correction is 9" down. In the formula, the distance between the sights and the distance to the target must be expressed in the same unit of measurement, but it doesn't matter what unit you choose. We'll keep it simple and say the distance between the sights is 3 feet.
The formuls is:
(distance between sights/distance to target) X desired correction in inches
(3/300) X 9 = .09"
Either the rear sight needs to be about .09" lower or the front sight needs to be about .09" higher. It might be easiest to install a higher front blade.
Hope this helps.

 

[ronnie01]

36" radius on 100 yds range you need .010" for 1 moa change in poi. 36÷3600=.010" will give you 1 minute of angle change (simple math sight radius in inches divided by range in inches will give you 1moa for any range)

 

[B_noser]

36" radius on 100 yds range you need .010" for 1 moa change in poi. 36÷3600=.010" will give you 1 minute of angle change (simple math sight radius in inches divided by range in inches will give you 1moa for any range)

I think we have said the same thing and come up with the same answer. Nine inches of correction at 100 yds is 9 moa and requires 9 x .010 or .090" of sight adjustment. We need to remember that 1 moa equals 1" at 100 yds only. One moa equals .0.75" at 75 yds and 1.5" at 150 yds. The formula, as I presented it, will work for any correction to poi at any range.

 

[BCRider]

Your title says "fixed sight"?

That's fine if the ammo matches this particular figure or whatever it might be for drop at 100. But a FIXED sight? I can't help thinking that there's going to be too much variation in ammo from brand to brand to allow a truly fixed sight to be fitted. Or you'll be locked into reloading with one weight and shape of bullet shooting at a very specific muzzle velocity. Or at best one bullet weight but with a few fairly closely related shapes that provide a small range of BC values so the drop can be set to more or less the same by the charge weight.

That all seems a bit limiting. I'd think you'd want to stick with an option that has at least some slight amount of adjustability of the rear sight. If your present rear sight is too tall then instead of replacing it with a shorter fixed sight I think I'd want to find a short adjustable option or fit a taller front sight to allow using the present adjustable rear.