The Firing Line Forums

Go Back   The Firing Line Forums > Hogan's Alley > Handguns: General Handgun Forum

Reply
 
Thread Tools
Old May 16, 2011, 04:31 PM   #1
Willie D
Senior Member
 
Join Date: June 24, 2007
Posts: 1,116
Handgun bullet trajectory - any general guidelines?

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?
Willie D is offline  
Old May 16, 2011, 06:10 PM   #2
jhenry
Senior Member
 
Join Date: May 27, 2006
Location: Ozarks
Posts: 1,813
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.
__________________
"A Liberal is someone who doesn't care what you do, as long as it's mandatory". - Charles Krauthammer
jhenry is offline  
Old May 16, 2011, 06:25 PM   #3
Doyle
Senior Member
 
Join Date: June 20, 2007
Location: Starkville, MS (new to MS)
Posts: 4,767
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.
Doyle is offline  
Old May 16, 2011, 06:34 PM   #4
Sleuth
Senior Member
 
Join Date: September 27, 2002
Location: Arizona
Posts: 445
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!
__________________
Sleuth
Sleuth is offline  
Old May 16, 2011, 06:43 PM   #5
spacecoast
Senior Member
 
Join Date: October 14, 2009
Location: Sunshine and Keystone States
Posts: 4,111
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.
spacecoast is online now  
Old May 16, 2011, 06:59 PM   #6
Dwight55
Senior Member
 
Join Date: June 18, 2004
Location: Central Ohio
Posts: 2,559
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
__________________
www.dwightsgunleather.com
If you can breathe, . . . thank God!
If you can read, . . . thank a teacher!
If you are reading this in English, . . . thank a Veteran!
Dwight55 is offline  
Old May 16, 2011, 10:42 PM   #7
Mike38
Senior Member
 
Join Date: December 28, 2009
Location: North Central Illinois
Posts: 1,160
Quote:
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.

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?
Mike38 is offline  
Old May 17, 2011, 12:32 AM   #8
Archie
Senior Member
 
Join Date: May 26, 2000
Location: Hastings, Nebrasksa - the Heartland!
Posts: 2,096
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.
__________________
There ain't no free lunch, except Jesus.
Archie

Check out updated journal at http://oldmanmontgomery.wordpress.com/
Archie is offline  
Old May 17, 2011, 07:35 AM   #9
spacecoast
Senior Member
 
Join Date: October 14, 2009
Location: Sunshine and Keystone States
Posts: 4,111
Quote:
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?
Physics dictates that there is some movement immediately. It doesn't take much.
spacecoast is online now  
Old May 17, 2011, 08:59 AM   #10
g.willikers
Senior Member
 
Join Date: September 28, 2008
Posts: 5,117
Mike38,
I agree.
There's many more things that will affect where the bullet goes than the recoil.
At least for the first shot.
__________________
Lock the doors, they're coming in the windows.
g.willikers is online now  
Old May 17, 2011, 09:36 AM   #11
Mello2u
Senior Member
 
Join Date: February 21, 2009
Location: Georgia
Posts: 1,424
Quote:
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?
#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.
__________________
NRA Life Member - Orange Gunsite Member - NRA Certified Pistol Instructor
"When plunder becomes a way of life for a group of men living together in society,
they create for themselves in the course of time a legal system that authorizes it and a moral code that justifies it.
" Frederic Bastiat

Last edited by Mello2u; May 17, 2011 at 03:00 PM.
Mello2u is offline  
Old May 17, 2011, 10:55 AM   #12
Mike38
Senior Member
 
Join Date: December 28, 2009
Location: North Central Illinois
Posts: 1,160
Quote:
Physics dictates that there is some movement immediately. It doesn't take much.
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.
Mike38 is offline  
Old May 17, 2011, 11:05 AM   #13
carguychris
Senior Member
 
Join Date: October 20, 2007
Location: Richardson, TX
Posts: 5,501
Quote:
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...
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.
__________________
"Smokey, this is not 'Nam. This is bowling. There are rules... MARK IT ZERO!!" - Walter Sobchak
carguychris is offline  
Old May 17, 2011, 11:12 AM   #14
Brian Pfleuger
Staff
 
Join Date: June 25, 2008
Location: Central, Southern NY, USA
Posts: 18,761
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.
__________________
Still happily answering to the call-sign Peetza.
---
The problem, as you so eloquently put it, is choice.
-The Architect
-----
He is no fool who gives what he can not keep to gain what he can not lose.
-Jim Eliott, paraphrasing Philip Henry.
Brian Pfleuger is online now  
Old May 17, 2011, 12:33 PM   #15
44 AMP
Staff
 
Join Date: March 11, 2006
Location: Upper US
Posts: 11,320
……..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.
__________________
All else being equal (and it almost never is) bigger bullets tend to work better.
44 AMP is offline  
Old May 17, 2011, 12:34 PM   #16
SRH78
Senior Member
 
Join Date: April 18, 2011
Location: Texas
Posts: 446
Quote:
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.
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.
SRH78 is offline  
Old May 17, 2011, 02:23 PM   #17
Mike38
Senior Member
 
Join Date: December 28, 2009
Location: North Central Illinois
Posts: 1,160
Interesting, thanks for the education.
Mike38 is offline  
Old May 17, 2011, 04:18 PM   #18
Clifford L. Hughes
Senior Member
 
Join Date: February 24, 2011
Location: Southern Californis
Posts: 795
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
Clifford L. Hughes is offline  
Old May 21, 2011, 10:33 PM   #19
1SOW
Senior Member
 
Join Date: December 2, 2007
Location: South TX
Posts: 269
Obviously the OP does care and made no mention of gunfights or SD.

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

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

Quote:
Finally, what effect does the 'hot-ness' of a powder charge have on changes on your POI?
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.

Last edited by 1SOW; May 21, 2011 at 10:45 PM.
1SOW is offline  
Old May 22, 2011, 09:34 AM   #20
WESHOOT2
Senior Member
 
Join Date: February 20, 1999
Location: home on the range; Vermont (Caspian country)
Posts: 14,237
eyeballin'

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

Just sayin'.....
__________________
.
"all my ammo is mostly retired factory ammo"
WESHOOT2 is offline  
Old May 22, 2011, 10:30 AM   #21
Brian Pfleuger
Staff
 
Join Date: June 25, 2008
Location: Central, Southern NY, USA
Posts: 18,761
Quote:
Originally Posted by WESHOOT2
One might notice in those high-speed photos that gases exit the muzzle before the projectile.

Just sayin'.....
A properly sized projectile should allow virtually no gas bypass. I suspect that the vast majority of the gases exiting the muzzle before the bullet are simply the air in the barrel being "chased" out by the bullet.
__________________
Still happily answering to the call-sign Peetza.
---
The problem, as you so eloquently put it, is choice.
-The Architect
-----
He is no fool who gives what he can not keep to gain what he can not lose.
-Jim Eliott, paraphrasing Philip Henry.
Brian Pfleuger is online now  
Old May 22, 2011, 10:39 AM   #22
WESHOOT2
Senior Member
 
Join Date: February 20, 1999
Location: home on the range; Vermont (Caspian country)
Posts: 14,237
suspect vs knowledge

High-speed photography allows us to literally observe gases exiting prior to the projectile.
"Should" and "suspect" are assumptions, and false. As the case expands into the chamber gases pass the projectile. The vast majority of exiting gases are a product of the powder's combustion.

If I only had the ability to post the evidence; I apologize for my inability.
__________________
.
"all my ammo is mostly retired factory ammo"
WESHOOT2 is offline  
Old May 22, 2011, 11:08 AM   #23
Brian Pfleuger
Staff
 
Join Date: June 25, 2008
Location: Central, Southern NY, USA
Posts: 18,761
I've seem high-speed video and pictures that show the gases exiting before the bullet. What I haven't seen is the evidence to determine the source. If you have, so be it. It seems to me that there would be too many variables to make a concrete statement that covers all cases.

If the bullet is properly sized, there should be virtually no bypass once it is engraved in the rifling.

If the chamber is "normal", or at least typical, and the bullets are of typical length, they should be engaging the rifling before they exit the case neck, thereby preventing gas bypass, or at least much of it.

Lead bullet shooters very often speak of preventing gas bypass in order to prevent "leading".

It sure seems to me like the amount of gas bypass is minimal under normal circumstances, certainly minimal enough that it's effect on recoil must be nearly nonexistent.
__________________
Still happily answering to the call-sign Peetza.
---
The problem, as you so eloquently put it, is choice.
-The Architect
-----
He is no fool who gives what he can not keep to gain what he can not lose.
-Jim Eliott, paraphrasing Philip Henry.
Brian Pfleuger is online now  
Old May 22, 2011, 11:23 AM   #24
PawPaw
Senior Member
 
Join Date: December 24, 2010
Location: Central Louisiana
Posts: 3,112
In the case of the common revolver cartidges, .38/.357 or .44Spec/.44magnum, there is a lot of gas that gets out while the bullet is in the barrel.

I'm no physicist, but I've been shooting revolvers for a long time, and I know that when I load a heavy-bullet special at 800 fps, then load a light-bullet magnum at 1300 fps, the faster bullet will hit lower on the target than the slower one. I've seen it happen many times in the past 30 years.
__________________
Dennis Dezendorf

http://pawpawshouse.blogspot.com
PawPaw is offline  
Old May 22, 2011, 11:27 AM   #25
9-ball
Senior Member
 
Join Date: May 21, 2011
Location: Belgium
Posts: 340
Little physics intermezzo

Okay, this is my first post on this forum, but since I'm a physics student, I tought I could sort this out.

Both Mark38 and Peetzakilla have some true points. You're just looking at it starting from other laws. According to the third law of dynamics which Peetzakilla used in his explenation, the momentum will stay the same in the whole system. This however is caused by the actions of the gas Mark38 explained. The only point he got wrong is that the bullet isn't part of the gun, so when the gas pushes in all directions, it pushes against the bottom of the casing and the bullet. Since the bullet has friction, a part of the pressure against the casing is compensated for by the friction of the bullet.

All of the force used to accelerate the bullet will be felt as recoil too. As the gun weighs roughly a hundredfold of the bullet, the weapon will go only one hundreth of the speed of the bullet in recoil. So while the bullet is acceleration from 0 m/s to it's v0, the "recoilspeed" of the gun will be in direct proportion to the speed of the bullet at that particular moment.

And now we're getting to the point. If we look at the generated recoil energy, we see that the part caused while the bullet is in the barrel is only 1/3th of the total recoil energy. The other parts caused by burning gasses when the bullet has exited.

So to sum it up, if someone would really want it, I want to calculate the rotational speed of a recoiling weapon. However, considering the facts I mentioned above, I'm pretty sure it would be fairly pointless, and it would most likely be in the range of some millimeters without any noticable effect in practical applications.

9-ball
9-ball is offline  
Reply

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 11:28 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
This site and contents, including all posts, Copyright © 1998-2014 S.W.A.T. Magazine
Copyright Complaints: Please direct DMCA Takedown Notices to the registered agent: thefiringline.com
Contact Us
Page generated in 0.15213 seconds with 7 queries