9mm travel distance - are my calculations correct?

R

Rich_357

New member
Given the following
A 9mm traveling at 1200ft/sec
Fired horizontally on level ground from 6ft
Gravity causing objects to fall at 32ft/sec
I'm calculating that said round will hit the ground in 225 feet?

6ft * 1sec/32ft =.1875 seconds before impact with the ground

.1875sec * 1200ft/sec = 225 feet.
 
You're mixing up acceleration and velocity when it comes to the rate of gravity and that's messing up your fall time estimate.

https://en.m.wikipedia.org/wiki/Equations_for_a_falling_body
https://www.angio.net/personal/climb/speed.html

From a practical standpoint your calculation is telling you that the round will impact the ground after only 75 yds. That should by itself seem wrong. There are more involved ballistic calculators out there if your Google-fu is strong.

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No problem. I had to look it up to remember.

The equation you want is:
t = sqrt( (2*d) / g).
Where t is time in seconds, d is the distance and g is the rate of gravity (making sure both d and g are in the same units in terms of imperial or metric). That gives:
t = sqrt( (2*6) / 32) = sqrt(12/32) = 0.61 sec.

This is matched by the value you can calculate at the link, where 6 feet ~= 1.829 meters.

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Rich_357 said:
@TunnelRat...I forgot that accelleration was squared. Thanks...been a bit since physics class.
Click to expand...
You and me both, though you probably have me beat. I loved General Physics but I don't use it much. Glad I could help.

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2 meters is a much taller shooter than I, especially as the pistol is at my shoulders more than my head. Certainly possible though for those of us not vertically challenged.

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I used 2 meters to be safe.
Height in meters 2
Mass in kg 0.00745
Speed at impact:6.26 m/s or 22.54 km/h
Time until impact:0.64 s
Energy at impact:0.15 joules

0.64sec*1200ft/sec=768ft. (Air resistance is going to slow that down.)
 
Things kind of dull where you are? snicker.
"How far will my rifle shoot?" is a chapter in Hatcher's Notebook. I think the formula is in there.
Bullet velocity isn't the only factor. Bullet weight and your altitude above sea level matters too.
Six feet is not 2 meters. It's close though. 6 feet is 1.83 meters.
Gravity doesn't affect falling objects at the same rate at different altitudes. There is no acceleration after the bullet leaves the barrel either.
 
T. O'Heir said:
Things kind of dull where you are? snicker.
"How far will my rifle shoot?" is a chapter in Hatcher's Notebook. I think the formula is in there.
Bullet velocity isn't the only factor. Bullet weight and your altitude above sea level matters too.
Six feet is not 2 meters. It's close though. 6 feet is 1.83 meters.
Gravity doesn't affect falling objects at the same rate at different altitudes. There is no acceleration after the bullet leaves the barrel either.
Click to expand...
Actually there is an acceleration, an acceleration downward due to gravity.

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TunnelRat said:
Actually there is an acceleration, an acceleration downward due to gravity.
Click to expand...
Technically, there is also acceleration in the horizontal plane after the bullet leaves the barrel. It just happens to be a negative acceleration, induced by air resistance. And if you want to try to take that into account, then you need to know the ballistic coefficient for the bullet.
 
Aguila Blanca said:
Technically, there is also acceleration in the horizontal plane after the bullet leaves the barrel. It just happens to be a negative acceleration, induced by air resistance. And if you want to try to take that into account, then you need to know the ballistic coefficient for the bullet.
Click to expand...
Good point.

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I once was talked into hitting a two-foot square plate, on two chains. Fastened at the top two corners, at 100 yards. On Palm Bay Police range. Glock 17 pistol, with TruGlo sights.

Me prone, my Son standing behind me, spotting. Used my carry ammo (Black Talon) 147g. Used a small sandbag as a rest.
My Son called hit, 3 out of three. But I could hear the hits, seemed like a couple of secs. To get there.
I aimed at the middle, my son said it looked like the rounds hit in the centre?
Just put the three green dots in a straight line, in the middle. No idea what drop?

Nanuk.

A shot from my Canadian Gun club, fired from sitting at the bench of the Bulls Eye range, cleared the top of the berm. Browning Hi-Power pistol, Sub Gun ammo. A new immigrant to Canada, in his garden in his calf. Went through his jeans. He went to the Hospital, Un-known pain?
Found the bullet. Easy to find out where it came from. A 1/4 of a mile.
 
Last edited:
You got it. From 6 feet it will take 0.612 seconds to hit the ground. At 1,200 fps will travel 734.4 feet or 244.8 yards. 6' = 16 (t x t)
 
Nanuk said:
A thinking man would be more concerned with how far it was dangerous.
Click to expand...
Then a "thinking man" would still need to do a similar calculation, except the end point is no longer when the bullet hits the ground but at what point has the bullet lost enough energy to no longer be able to pierce human flesh. My guess is it will hit the ground from the height of a shooter with enough force to still be harmful to a person. If someone wants to run the calculation of what the velocity is when it strikes the ground we can go from there.

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