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Someone help me with the math on this...

2K views 10 replies 7 participants last post by  Iowegan 
#1 ·
Wasn't sure if this is the correct forum, but here is the question

If I fire a bullet in my 45ACP that leaves the muzzle at 900fps, and at 25 feet I am dead center on target, how low will I be at 50 yards?

And the more difficult question; if I set my sights so that I am 1" high at 25 feet, how low will I be at 50 yards?

Doesn't have to be so exact that variables like coefficient of drag need to be calculated, just a general number based on 900fps at the muzzle.
 
#3 ·
Intereting chart. According to my input, if I am sighted in at 10 yards I drop 1.8" at 50 yards.

But if I sight in at 20 yards, I drop 2.8" at 50 yards. Sort of contrary to my thoughts, I need to work on this...
 
#5 ·
Shooting solution on a 45 automatic , ( according to my 45 auto.)
If your shooting at me :
@ 20 yards ,,, I'm running.
@ 50 yards ,,, I'm pretty nervous and will probably flinch
@ 75 yards ,,, I'll probably stand there and spot for you.
@ 100 yards ,, I'm probably going to loose interest and take a nap.

On a 45 cal. Blackhawk with a 7.5 barrel, @ 50 I'm running.

LOL.

seriously though, Maybe it has something to do with where the bullet hits the top of its apex in flight. This is much more noticeable on a long range rifle. MAYBE ? ?
 
#8 · (Edited)
trooplewis, There are two scenarios, the first being a "normal trajectory". This is when the muzzle is pointed up slightly where the bullet will rise, cross the line of sight at a given distance, reach peak trajectory, then start dropping and cross the line of sight again farther downrange.

The second scenario is when the muzzle is pointed up very slightly and the bullet reaches peak trajectory at your sight-in distance, thus only crossing the sight line once.

First scenario (normal trajectory): According to Ballistic Explorer, if you sight in your 45 ACP (900 fps, front sight is 1/2" above bore line) at 26 yards, the bullet will cross the sight line at 25 feet, rise to a peak trajectory of .2" at 17 yards, then drop back to the line of sight at 26 yards. At 50 yards the bullet will be 2.3" low.

Second scenario: If the sights are adjusted to intersect the sight line at 25 feet (peak trajectory), at 25 yards the bullet will be .2" low and at 50 yards, it will be 2.6" low.

Second question .... when sighted for 1" high at 25 feet, the bullet will be 4.3" high at 50 yards. Why? The muzzle has to be pointed up more to get a +1" zero at 25 feet. It will reach peak trajectory at 40 yards then start dropping until it crosses the line of sight again at 85 yards.

The best option for sight adjustment with a 45 ACP is a 35 yard zero. This will result in a bullet path that is never less than .5 inches low, nor more than .5 inches high (about 1 bullet diameter) from the muzzle to 40 yards and will be 1.5" low at 50 yards.
 
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#9 ·
excellent explanation.
 
#10 ·
Thanks Iowegan. I like the 25-foot sight in option the best. I don't see myself in a situation when I would be firing at something (at least with a 45ACP) more than 75 feet away. But even so, 2.6" low at 50 yards is not a bad gamble.
 
#11 ·
trooplewis, Most handguns shoot surprisingly flat at distances out to 40 yards or so. As such, the most popular concept for sight adjustment is called "point blank", which means you aim directly at the target ... no hold over or hold under, and let the trajectory work for you. I used Ballistic Explorer to find the optimum sight in distance for a 45 ACP @ 900 fps (bullet weight does not matter ... gravity works the same for all weights).

Turns out, a 35 yard sight-in zero will give you the optimum trajectory where the bullet path is never more than one bullet diameter (.45") from the sight line at distances ranging from the muzzle to 40.7 yards. The bullet first crosses the sight line at 19 feet (6.33 yds), reaches a peak trajectory of +.45" at 20 yards, drops back to the zero sight line at 35 yards, then drops to -1.5" at 50 yards.

Although Ballistic Explorer is very accurate, the gun probably won't group tight enough to confirm the trajectory at farther distances. I would recommend sighting in for dead zero at 19 feet where groups will be the tightest. Here's a Ballistic Explorer bullet path chart that shows the above trajectory:

 
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