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Old May 20, 2007, 06:29 PM   #1
Evil Dog
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Point of Impact Change with velocity change?

Was just wondering if any given bullet would print higher (or lower) with velocity increase presuming no change in sights? Would the a bullet traveling at say 1000fps print in the same place when traveling at say 800fps if there were no sight adjustment?
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Old May 20, 2007, 06:42 PM   #2
amamnn
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yes and no. Generally, a velocity increase will result in a flatter trajectory. Depending upon where your POA and POI are along the trajectories, the POI may change. It can seem like you're not doing much for the trajectory when shooting at close ranges as in handgun shooting.

For example, a trajectory that crosses the extended POA (aim line drawn from sight to zero point) at 20 and 100 yards (zero @ 100 yards) may not seem different from one that crosses at 25 yards. The POI on a target set out at 25 yards will look pretty much the same for both. If you are shooting at 100 yards it should look different, all other things being equal.
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Old May 20, 2007, 06:52 PM   #3
Evil Dog
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Ah... I should have been a little bit clearer in my question... I was referring to a pistol with fixed sights.
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Old May 20, 2007, 07:12 PM   #4
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The slower bullet could print higher do to its longer dwell time in the barrel but with less recoil maybe not
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Old May 20, 2007, 09:21 PM   #5
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Check out this trajectory calculator - http://www.cs.utah.edu/~zachary/isp/...on/Cannon.html
> hit the yellow button. If you change the initial velocities, and compare trajectories based on the same firing angle and value for gravity, you'll see how the point of impact changes as you increase the velocity. Imagine that one of the vertical distance lines is the face of a target.

* use the arrow buttons, it doesn't recognize numbers that you type into the fields.

Basically for identical bullets leaving the muzzle at 1000fps vs 800fps, the 800fps bullet will fall farther by the time it reaches the target. So it will hit the target lower than a bullet traveling at 1000fps. For closer targets, the divergence in trajectories isn't as great and so the difference in points of impact isn't as apparent.
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Old May 20, 2007, 09:29 PM   #6
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That simulator assumes the faster and slower bullet leave the barrel at the same angle. Might not be the case.
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Old May 20, 2007, 10:12 PM   #7
PeteQuad
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All bullets leave the barrel at the same angle - straight out.

An identical bullet travelling faster will hit the target higher given no change in sights, but for short range pistol shooting I doubt you will notice much difference.
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Old May 20, 2007, 10:16 PM   #8
Dave Haven
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Re: jibjab

Quote:
The slower bullet could print higher do to its longer dwell time in the barrel but with less recoil maybe not
^YUP!
A few years ago an engineer at work was telling me about sighting-in a .357 Magnum with .38 Special loads.
"Then when I switched to .357 Magnums, and.."
"It shot lower, didn't it?"
"Yeah! Why IS that?"
He understood that explanation within 10 seconds.
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Old May 20, 2007, 10:17 PM   #9
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A slower bullet will be in the barrel longer, giving recoil more time to elevate the barrel. This will mean higher impact at shorter ranges, but the velocity loss will mean lower impact at longer ranges (more arcing trajectory). So there isn't any one answer. It will depend on range, the mass of the gun and the bullet and how tightly you are able to hold on to the gun. With this many variables, your best bet is to try it and see what you get? In my general experience, at ranges 25 yards and under, these variables only amount to an inch or so difference in POI. For a given weight, it is too little difference to matter in practical combat shooting, but enough to make a target shooter tweak his sight settings.

Nick
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Old May 21, 2007, 12:41 AM   #10
PeteQuad
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Sorry, I had assumed a benchrest state for the firearm. If you are talking about how it would effect someone actually firing the firearms, as in would they flinch more from recoil or be able to control it less, well, I guess it would depend on the shooter (and the gun, barrel length, weight, caliber, etc.).
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Old May 21, 2007, 04:33 AM   #11
685cmj
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I have kept very careful track over a long time (and all the targets) of my shooting with +P and regular .38 loads. The regular .38 loads always shoot significantly higher than the .38+P, even indoors with close in targets (25 feet and less).
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