Does anyone have a formula to figure out the subtension(sp?) of a front sight on a target at X yards.

It's just a similar triangles problem:

(sight width)/(Eye to sight distance) = (target coverage)/(Eye to target distance)

Remember to use the same units for all values, i.e. inches.

This is really why they taught us this crap in school. It wasn't so we could become rocket scientists or brain surgeons. I'd bet there are way more shooters than rocket scientists.

Thanks John, I should've thought of that myself but evidently had a brain fart.

I spoke too soon, looks like We'll have to modify the formula. I plugged in the following numbers sight width-.124, eye to sight-27.5, eye to target-1836, all in inches and ended up with a value of 8.278 inches, this is quite a bit more than my S&W covers at 50 yards. What have I done wrong?

[QUOTE]Originally posted by Lewis50:
I spoke too soon, looks like We'll have to modify the formula.

Have you tried it at the range? The formula seems to be correct, and as an example my 45-70 sight subtends 8" at 100 yards. That is on a 28" barrel. I haven't done the math on that rifle, but 8" at 50 yards seems reasonable on a pistol.

While target shooting yesterday at a 3" orange dot useing a 6-o'clock hold from the bench, I noticed the front sight was very close to that width when I superimposed it on the dot at 50 yards. The point of this exercise is to come up with the theoritical subtention so I can make a square box that is the same observed width as the sights at any given range, then with a 6-o'clock hold the horizontal sight displacement would be easier to see. I agree with you that 8" seems correct for 100 yards, just too wide for 50.

Mea Culpa,
I just set up a calibrated target at 50 yards and the formula is correct, the front sight appears to be a bit over 8" wide. I guess my memory from yesterday is failing as fast as my eyesight. Thanks again JohnD.

I wrote a very small & simple program to make the calculations. You just need to enter the sight radius (distance between front & rear sights)of your rifle and the program will tell you the rest.

I can e-mail it to you (or anyone else for that matter) if your interested. Me e-mail is Sean.Kettley@nscc.ca.

Cheers,

kettlesd