Handgun bullet trajectory - any general guidelines?

W

Willie D

New member
I sometimes read comments along the lines of "lighter bullets tend to hit lower" and I was wondering if there any rules of thumb regarding the effects of bullet weights on trajectory (fired from the same gun).



So a 115gr 9mm round should hit lower than a 124gr bullet if both are fired at the same point of aim?


What about when switching between .38 and .357?



Finally, what effect does the 'hot-ness' of a powder charge have on changes on your POI?
 
Assuming they are fired on the horizontal, any bullet, caliber, velocity combination from any firearm, will hit the ground at the same time, if fired at the same time. The difference will be the amount of real estate covered prior to impacting the earth. The flatter shooting stuff goes further in the same amount of time.
 
What Jhenry said, but you also have to factor in the angle of the barrel at the time the bullet leaves the barrel. That's where the heavier bullet - bigger recoil comes in. Starting point of a higher angle means a different point of impact even not accounting for differences in bullet speed over ground.
 
At the distances involved in a life-or-death encounter, none of this matters. You are moving, your target is moving, and 80+ % of the time, you are at 7 yards or less!
 
Heavier bullets tend to move slower, which gives the barrel more time to tilt up from recoil. Hence the tendency to hit the target higher.
 
A plotted trajectory's (graphed out) will stretch out further if the first projectile is going faster than the second projectile.

If they are traveling the same speed, the weight will not change the graph.

Having said all that, . . . my 1911 shoots about 1 foot high at 100 yards using Winchester Whitebox 230 grain FMJ. In reality for me, . . . THAT is what I needed to know.

May God bless,
Dwight
 
Heavier bullets tend to move slower, which gives the barrel more time to tilt up from recoil. Hence the tendency to hit the target higher.
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I have a question. I'm sure most everyone here has seen films of super high frame per second cameras slowed way down so you can watch the bullet exit the barrel. I watched one of a M1911, must have viewed it 100 times, trying to educate myself on exactly what happens durring firring. Far as I can tell, the bullet exits, and is at least 10 inches or more from the muzzle before any detectable movement or recoil is seen. So how is it that the heavier bullet shoots higher when there is zero movement of the barrel until after the bullet is well on it's way to the target?
 
Hello Willie

Frankly, handgun trajectories at general handgun ranges are pretty flat.

Yes, they do curve in a path called a parabola, but only over distance. Consider: According to the table at http://www.chuckhawks.com/handgun_trajectory_table.htm a .45 ACP 230 grain hardball round - not famous for being a long range cartridge - when sighted in to strike 2.6 inches high at 25 yards, drops a monstrous 6.9 inches below the point of aim at 100 yards. So that's a nine and one half inch difference between 25 and 100 yards.

Most shooters can't shoot a ten inch group with a pistol at 100 yards, so there's no way to tell if the miss was because the sights aren't right or one just missed.

Bullet impact rises from the muzzle, because a pistol - or rifle - is actually pointed 'up' a bit. The muzzle is inclined so the bullet's path rises above the line of sight and then begins falling back and hopefully gets back to the line of sight exactly at the place one wants the bullet to strike. 25 or 50 yards for bullseye shooters, for instance.

The useful range of any round depends on the target. For paper or metal targets, getting bullet (point of impact) and target (point of aim) aligned is a mathematical problem; and starting points can be assumed or guessed in many cases. Then shooting is done to perfect the sight settings. For hunting game, one learns the outer limits of accuracy and sufficient power and then learns to estimate range and hold-over or under.

However, for self defense, a Government Model 45 ACP will generally hit a silhouette target out to 100 yards if the shooter can hold accurately. For deer hunting with a handgun at ranges out to 50 yards, the trajectory is essentially line of sight.

There are books on trajectory. I must confess I cannot recall any of them right now - except "The Bullet's Flight" by Mann. It's pretty technical, but covers the subject well. Amazon has one, a collector's item, for $200 or so.

You will learn more by simply learning to shoot well and keep notes of your targets, sight settings and experiences. Keep track of weather and lighting conditions, too. Bright light changes the way one's eyes see the sights. That in turn makes it seem the gun and ammo is shooting higher or lower. Or even off to the side if the light is low and angling from the side.
 
So how is it that the heavier bullet shoots higher when there is zero movement of the barrel until after the bullet is well on it's way to the target?
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Physics dictates that there is some movement immediately. It doesn't take much.
 
Willie D

Handgun bullet trajectory - any general guidelines?
I sometimes read comments along the lines of "lighter bullets tend to hit lower" and [#1] I was wondering if there any rules of thumb regarding the effects of bullet weights on trajectory (fired from the same gun).

[#2] So a 115gr 9mm round should hit lower than a 124gr bullet if both are fired at the same point of aim?

[#3]What about when switching between .38 and .357?

[#4] Finally, what effect does the 'hot-ness' of a powder charge have on changes on your POI?
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#1 - General rule - A slower velocity bullet takes longer to exit the barrel, so the barrel has more time to rise before the bullet exits on its path outside the barrel on the trip down range.

#2 It depends many factors including but not limited to distance, muzzle velocity, and ballistic coefficient. Generally, if you are only talking about short range (under 10 yards) then yes. But if you are talking about all ranges then no. At some point external ballistics become more of a factor than the different angles at muzzle exit between two bullets. It is not merely weight but velocity and ballistic coefficient that have different effects on external ballistics. A 160 grain semi wad cutter design might have a lower ballistic coefficient than a 150 grain hollow point bullet design of the came caliber. It is possible that there may be some combination of factors which leads to the result where a lighter weight bullet strikes higher than a heavier bullet at 50 yards; even when the same heavier bullet strikes higher at 10 yards.

#3 Same factors.

#4 Define hot-ness.
 
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Physics dictates that there is some movement immediately. It doesn't take much.
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Fair enough. But, the movement is caused by the rapidly expanding gases from the burning gun powder. The forces created from this rapidly expanding gas doesn’t go only in one direction, rearwards or forwards, it goes in all directions. Equal pressures are going forward, rearwards, up, down, to the left, to the right, (you get the idea). As the bullet moves out of the case mouth and down the bore, there are still equal pressures in all directions, equaling / evening out any movement called recoil. Once the bullet exists the muzzle, then and only then does the equal and even pressures change from all directions to forwards and backwards only. Then and only then is there felt recoil and muzzle flip, and once the bullet has left the bore, the shooter could fall on his butt and it wouldn’t effect the flight of the bullet.

There can not be movement when pressures are equal in all directions. Movement happens only when there is a pressure drop in one direction, then the movement travels in an opposite direction. Once the bullet exit’s the barrel, there is a pressure drop going forward. The pressure stays the same going rearwards, which then causes felt recoil. But that recoil doesn’t matter, because the bullet has already left the barrel.


……..or I have no idea what I’m talking about, which could very well be true.
 
Bullet impact rises from the muzzle, because a pistol - or rifle - is actually pointed 'up' a bit. The muzzle is inclined so the bullet's path rises above the line of sight...
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This is true of rifles, but with most handguns, the barrel is actually pointed slightly downwards when the sights are lined up. This is meant to compensate for the muzzle rise that occurs before the bullet leaves the barrel.

This fact comes up regularly in the "Revolver" subforum, often from a new owner of a snubby, because the barrels of these guns usually have a very prominent and noticeable downwards angle. This is necessary to compensate for these guns' generally light weight.

This is less noticeable with most modern centerfire automatics because the barrel is usually hidden inside the slide. However, you can sometimes notice it by field-stripping the pistol and placing the barrel in firing position atop the stripped frame.
 
Mike38,

Your physics is suspect there... It's not gas pressure that causes the early stages of recoil, it's conservation of momentum.

The entire "system" of gun and bullet starts with zero momentum. When the powder is ignited the unbalanced pressure (a lot behind the bullet, roughly 14.7 pounds in front of it) causes the bullet to accelerate. Acceleration is a change in momentum. This change is equalized by an acceleration of the gun in the opposite direction, keeping total momentum at zero.

The time when the pressure matters to recoil is when the bullet exits and "uncorks" the barrel. The high pressure gases are then free to expand much more rapidly than they could push the bullet, creating what amounts to a rocket.
 
……..or I have no idea what I’m talking about, which could very well be true.

You know what you are talking about, BUT you are leaving out an important thing. The grip.

The thing with handguns (germaine to this discussion) is that they are held. And they are held well below the axis of the bore.

Physics says equal force in all directions, quite true. However, the amount of movement from that equal force is determined by the masses involved, and their ability to move.

By holding the pistol well below the line of the bore, the recoil forces the gun to rotate around the grip. And ths movement begins (undetectable to the eye) as soon as the bullet begins moving. If the grip was directly behind the axis of he bore, all the movement would be straight back, which is why rifles, with much greater recoil energy (and not fully balanced by their greater weight) show less muzzle rise, proportionally. With the rotational axis of the handgun so far below the line of the bore, muzzle rise is more pronounced.

The barrel of a handgun begins to rise as soon as the bullet starts moving down it. Now, we are talking very small amounts of movement,in very, very short periods of time, and it takes some very sophisticated instruments to measure the actual amount, but it does happen.

Add in the intentional arc of the bullet flight (as compared to the straight line of sight) and at regular pistol ranges, heavier bullets do tend to strike the target higher than lighter ones. The amount varies with many variables, but in general, its true and constant. And remember that the higher or lower is only in relation to your line of sight and point of aim. And that it also varies with the distance to the target.

For example, a 25yd bullseye, gun X, sighed to hit dead center with a 160gr bullet at xyz fps could give you hits in the 7 or 8 ring (low) on the target with a 125gr bullet at ABC fps, with the same sight picture. Because, typically, the lighter bullet is moving considerably faster, spending less time in the bore, so its path due to the recoil raising the barrel, is lower. Also, the physics of mass do apply, reducing the amount of recoil energy (a tiny fraction) thereby reducing the muzzle rise a corresponding amount.

For a target shooter, or a hunter (especially small game) this is a significant thing to know, as that half inch (or whatever) could be the difference between winning the match, or missing the vitals of the animal. For a defensive shooter, at typical ranges, it is far less critical, and the amount of difference in the bullet impact is often well within the margin of error of the shooter.

Want a good field demonstration? Carefully shoot two groups, one with each bullet weight, on the same target, with the same point of aim. No rush, mark each shot on the target between groups. Then see how many of the shots overlap between the two. Odds are some will. Again, the specifics depend on many things, range to the target is one important one, but at typical defensive distances, odds are you will be in the right place with both bullet weights.
 
Your physics is suspect there... It's not gas pressure that causes the early stages of recoil, it's conservation of momentum.

The entire "system" of gun and bullet starts with zero momentum. When the powder is ignited the unbalanced pressure (a lot behind the bullet, roughly 14.7 pounds in front of it) causes the bullet to accelerate. Acceleration is a change in momentum. This change is equalized by an acceleration of the gun in the opposite direction, keeping total momentum at zero.

The time when the pressure matters to recoil is when the bullet exits and "uncorks" the barrel. The high pressure gases are then free to expand much more rapidly than they could push the bullet, creating what amounts to a rocket.
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Well said.

The more recoil a round produces, the more the the barrel moves before the bullet exits the bore. Heavy bullets also take longer to exit the barrel allowing more time for the barrel to move. If you take light 38's and heavy 357's in the same gun you will get a noticeable difference in poi if you have a loose grip. Do the same with 45 Colt's and full power 454 Casull rounds and the difference goes from noticable to huge.
 
Clifford L. Hughes

Willie D:

If you zero your pistol and then put a laser in the barrel you will find that the bore is pointed lower theh the sights. This is because the bullet is in motion during recoil. Light bullets accelerate faster and they leave the bore sooner thus striking lower than a heavy bullet. My Smith & Wesson modle 29 shoots 240 gr. lead bullets excellently. When I tried some 300 grain bullets, with the sights run all the way down, my bullets hit over a foot high at 25 yards.

Semper Fi.

Gunnery sergeant
Clifford L. Hughes
USMC Retired
 
Obviously the OP does care and made no mention of gunfights or SD.

So a 115gr 9mm round should hit lower than a 124gr bullet if both are fired at the same point of aim?
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No. Depends on the load/powder used.

What about when switching between .38 and .357?
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Ditto

Finally, what effect does the 'hot-ness' of a powder charge have on changes on your POI?
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Now we're down to the nitty griity. "Hotness" can mean TWO different things.
"Powder Burn Rate" can be VERY fast (Hot/fast powder) and still have a very light load, OR a slow burning powder can have a very heavy load.

The fast burn powder will build it's 'higher' pressure quickly. In 9mm works well up to 'about' 124-135 gr bullets . The slower burning powder (lower pressures) may still be building pressure/accelerating the bullet as it leaves the barrel. In 9mm a somewhat slower powder may work better for 147gr bullets. Check the load data and this should be reflected there. As an example compare Win 231 with HS-6, or Vit N310 with Vit N350.

All of these powder characteristics can be used to the shooter's advantage to 'make' POA = POI at a given range with a number of different type and weight bullets.

The fast burning pistol powders make good target/light loads--lower velocities. The slower burning powders make good SD loads--higher available velocities.

Hope this makes sense.

P.S. The slower burning powders will tend to shoot higher.
 
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eyeballin'

One might notice in those high-speed photos that gases exit the muzzle before the projectile.

Just sayin'.....
 
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