Sometimes it's good to know how much area your front sight covers at a given distance and with just a few measurements it's fairly easy to figure. We all know that when we look at something at a distance, it appears smaller. A bullseye that looks large at 25 yards isn't so large at 100 or 200 yards. Also, that front sight tends to cover more area at 200 yards. But how much? Simple.
The first thing we need to do is measure the width of the front sight. For example, on my Handi-rifle with a 22" barrel, the Williams firesight bead I've installed has a measured width of 0.091" (measured with my calipers). I've also determined that when the rifle is shouldered in firing position, the sight is 30" from my eye. So, what I've described is an isosceles triangle, 30" long and 0.091 inches wide. How much width would that sight cover (subtend) at 100 yards? Simple. 100 yards is 3600 inches, and the equation looks something like this:
0.091/30 = X/3600. Solve for X.
So, if my math is correct, that 0.091 front sight, 30 inches from my eye, will hide 10.92 inches at 100 yards. It's good to have that knowledge when I take the rifle afield. Now, how might we use that information?
If a deer's heart/lung area is 18 inches wide, then the front sight will completely cover that eighteen inches at about 150 yards. So, if when I put my rifle to my shoulder, I can see boiler room on either side of the sight, then I'm probably within 150 yards of that animal. Of course, all distance estimates are just that... estimates. Still, it's good to have that little bit of extra knowledge.