Re: Balllistics Program Question
Let´s have an aspirin together [img]images/icons/smile.gif[/img]...
If you are firing a 308 with a 175 SMK bullet @ 2680 fps, standard conditions and zero altitude, drop at 100yds is 2.53", and let's say sight height is 1.6" (this example is with the Sierra Infinity program, but exact numbers are not important).
In order for line of sight to coincide with the bullet trajectory at 100yds, you have to slope down your line of sight (or the erector tube inside the scope) to compensate for the sight height and the bullet drop at that distance. This compensation is 2.53+1.6 = 4.13" in 100yds.
Using a little trigonometry, we find that the proyection of the bore line crosses the line of sight at 38.74yds, and this means that the bore is pointing high 4.13*9.6126 = 39.7" at 1000yds.
If you substract this value from your drop at 1000yds (424.1") you have the bullet path relative to the line of sight at this point: 424.1-39.7 = 384.4". So, our sight correction for 1000yds would be 36.7 MOA.
Corrections to bullet drop at 100yds for air temperature, pressure and altitude are too small (this means the bullet keeps the same 100yds zero), but this same round fired at 20ºF could easily be going 100 fps slower (2580 fps), so the bullet drop is now 2.72". Using the above calculations we see this causes a 2.72*2.53 = 0.19" variation in our 100yds zero, and a 0.19*9.61 = 1.83" variation at 1000yds, this is a 0.17 MOA error at 1000yds, IMHO this is "lost in the noise", even with this extreme environmental change.
Edited for correctness...
[ 01-08-2003: Message edited by: TiroFijo ]