I've read that heavier bullets tend to have a higher point of impact, but shooting my Glock 29 I've found the opposite to be true. 200gr bullets shoot to point of aim, while 135gr bullets shoot 4" high at only 25 feet. I can understand seeing this much difference at 50 yards or something, but not at only 25 feet. Is this due to velocity or bullet weight? Also, on a gun with non adjustable elevation like a Glock how to you adjust for this?
How do bullet weights and velocity affect point of impact?
- Thread starter C Philip
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Think of what occurs once you ignite the powder In a cartridge. The expanding gas pushes the bullet from the chamber alongthe barrel and eventually out of the muzzle. This takes time. How much time depends on the accelleration and velocity of the bullet; as well as, the length of the barrel. While the bullet is traveling inside of the barrel, the firearm is recoiling. How much recoil depends on a multitude of factor which not only include the mass of the bellet, the mass of the ejects, and their velocities, also the mass of the firearm, and the distance that the barrel is in relation to the wrist joint.
Generally speaking, the slower bullet spends more time traveling in the barrel. If the recoil is the same compared to a faster lighter bullet, that lighter bullet will exit the barrel before the barrel has climbed as much as the slower heavier bullet. However, this assumes the same amount of muzzle climb and recoil in both instances. This is assuming a lot. This may or may not occur with the loads you actually shoot in your gun.
Another huge factor is the trajectory of the bullets once they exit the muzzle.
It is complicated.
Generally speaking, the slower bullet spends more time traveling in the barrel. If the recoil is the same compared to a faster lighter bullet, that lighter bullet will exit the barrel before the barrel has climbed as much as the slower heavier bullet. However, this assumes the same amount of muzzle climb and recoil in both instances. This is assuming a lot. This may or may not occur with the loads you actually shoot in your gun.
Another huge factor is the trajectory of the bullets once they exit the muzzle.
It is complicated.
no matter how fast an object travels it will fall to the earth at the same rate if no other forces are present( ie lift like an airplane wing)
lighter bullets travel faster than heavier ones all else being equal
therefore lighter bullets will travel a given distance faster thus less time to fall and a high POI on the target
clear as mud?
lighter bullets travel faster than heavier ones all else being equal
therefore lighter bullets will travel a given distance faster thus less time to fall and a high POI on the target
clear as mud?
ome more thing to consider
And that is the bullet weights you said you are shooting. Back in the old days, the difference between the lightest and heaviest bullets commonly used in a given caliber was not that much. This was before ultra light, and ultra heavy bullets got as popular as they are today. The 9mm ranged from 115gr to 124gr, although handloaders could load 90gr. The .38/.357 usd 125/130 to 158gr as standard. 110s were rare, and 180s unheard of, except for cast bullets, where a 200gr .38 was used (often with poor results) for years by police. The .45ACP went from 180 to 230, the .44mag from 180 to 240gr (300grs was not even considered in those days).
I think you might be seeing such a pronounced difference because the light bullet is only 5/8 the weight of the heavy one.
And that is the bullet weights you said you are shooting. Back in the old days, the difference between the lightest and heaviest bullets commonly used in a given caliber was not that much. This was before ultra light, and ultra heavy bullets got as popular as they are today. The 9mm ranged from 115gr to 124gr, although handloaders could load 90gr. The .38/.357 usd 125/130 to 158gr as standard. 110s were rare, and 180s unheard of, except for cast bullets, where a 200gr .38 was used (often with poor results) for years by police. The .45ACP went from 180 to 230, the .44mag from 180 to 240gr (300grs was not even considered in those days).
I think you might be seeing such a pronounced difference because the light bullet is only 5/8 the weight of the heavy one.
If recoil is equal the bullet that spends longest in the barrel will hit higher on the target since that gives the recoil impulse longer to lift the muzzle before the bullet exits the barrel.
So if you're comparing loads that recoil about the same amount the heavier bullet will be going slower, will spend more time in the barrel and will hit higher on the target at typical pistol ranges.
If one of the loads recoils MARKEDLY more than the other load it will probably print higher on the target. The much harder recoiling load bumps the muzzle upward much harder as the gun recoils and will result in the muzzle being higher when the bullet exits.
In your case you are comparing two VERY different loadings for the 10mm. I'm guessing that the 200gr loading is probably a practice loading, is fairly light for caliber and doesn't create a lot of recoil while the 135gr is probably loaded to full power, probably kicks pretty good and has a lot more muzzle flip.
So if you're comparing loads that recoil about the same amount the heavier bullet will be going slower, will spend more time in the barrel and will hit higher on the target at typical pistol ranges.
If one of the loads recoils MARKEDLY more than the other load it will probably print higher on the target. The much harder recoiling load bumps the muzzle upward much harder as the gun recoils and will result in the muzzle being higher when the bullet exits.
In your case you are comparing two VERY different loadings for the 10mm. I'm guessing that the 200gr loading is probably a practice loading, is fairly light for caliber and doesn't create a lot of recoil while the 135gr is probably loaded to full power, probably kicks pretty good and has a lot more muzzle flip.
As mentioned, all objects, regardless of mass, will fall at the same rate..given there are no conditions in which outside forces are introduced.
The POI of a round is directly related to the angle theta that the projectile is launched at.
An object of higher mass will indeed have a slower initial velocity, causing its angle upon exit to be noticeably higher...reason being, as John mentioned, is because the recoil has more time to effect the angle of the barrel upon exit.
The POI of a round is directly related to the angle theta that the projectile is launched at.
An object of higher mass will indeed have a slower initial velocity, causing its angle upon exit to be noticeably higher...reason being, as John mentioned, is because the recoil has more time to effect the angle of the barrel upon exit.
Considering the time a bullet spends inside the barrel (4" barrel at 900fps = 0.37037 milliseconds), I find it incredibly difficult to attribute that as a pivotal, or even remotely viable criteria for this discussion.
Care to post something scientific to substantiate these claims?
Care to post something scientific to substantiate these claims?
Diamond LawDawg
New member
Gravity
I understand...no matter what gun I fire 22---45 I aim,squeeze zeeeee trigger and hit exactly relative to that point. bullet weight,powder charge does effect distance..but that's left to those with a PHD. behind there names
I understand...no matter what gun I fire 22---45 I aim,squeeze zeeeee trigger and hit exactly relative to that point. bullet weight,powder charge does effect distance..but that's left to those with a PHD. behind there names
First semester physics... Gravity is always present and always pulls down at an acceleration of 9.8 meters per second, per second. This means that for the first second, the bullet is going to drop 9.8 meters, but for the second second, it's going to drop 19.6, and the third it would drop 29.4. So for 3 seconds of travel, the bullet has dropped 58.8 meters and is accelerating towards earth.
The time the bullet is in flight is pretty short, so the distance traveled has to be calculated into that to determine drop. It has nothing to do with bullet weight, it has to do with how fast the bullet is moving as that is the only variable which will affect the vertical location when that bullet arrives on target. (excluding outside factors such as wind)
Trajectory is explicitly a calculation of velocity over time in relation to gravitational pull. If the bullet slows down at a given rate over the distance it's traveled (which is not linear, meaning it's slowing down more and more the longer it's in flight due to aerodynamic drag), the drop will increase accordingly because the bullet hasn't made it as far in the same period of time.
This means that POA/POI is going to vary depending on how fast the given bullet travels relative to the POA/POI of the bullet the gun sights are set to. It's very simple to see this when you look at zeroing a rifle scope. It's also why some manufacturers include multiple height front sights with their hand guns - the bullet speed is going to determine which height is going to put that bullet on target.
Heavier bullets simply account for more inertia to overcome by the charge to accelerate a given bullet and as such either need more power behind them, or will travel slower.
Seriously folks, this ain't rocket science.
The time the bullet is in flight is pretty short, so the distance traveled has to be calculated into that to determine drop. It has nothing to do with bullet weight, it has to do with how fast the bullet is moving as that is the only variable which will affect the vertical location when that bullet arrives on target. (excluding outside factors such as wind)
Trajectory is explicitly a calculation of velocity over time in relation to gravitational pull. If the bullet slows down at a given rate over the distance it's traveled (which is not linear, meaning it's slowing down more and more the longer it's in flight due to aerodynamic drag), the drop will increase accordingly because the bullet hasn't made it as far in the same period of time.
This means that POA/POI is going to vary depending on how fast the given bullet travels relative to the POA/POI of the bullet the gun sights are set to. It's very simple to see this when you look at zeroing a rifle scope. It's also why some manufacturers include multiple height front sights with their hand guns - the bullet speed is going to determine which height is going to put that bullet on target.
Heavier bullets simply account for more inertia to overcome by the charge to accelerate a given bullet and as such either need more power behind them, or will travel slower.
Seriously folks, this ain't rocket science.
This is an oversimplification on a couple counts. The bullet weight will effect the trajectory as a heavier bullet will shed velocity slower than a light bullet. The weight vrs. dia. of any bullet is also a factor in calculating aerodynamic drag. The resulting ballistic coefficient (also effected by the profile), will change the rate of velocity loss.
Neither of these factors matters much from a practical perspective at the distances in this discussion. At longer ranges both issues will become more pronounced. I only point it out to illustrate it is not as simple as it seems at first glance.
In the ranges specified in the original question, I would support the muzzle rise theory. I have not seen data on the rate and speed of muzzle rise on a given gun and projectile combination so I could not do the math to support it.
You know Pete, I had figured someone would call me on that. 
Bullet mass and subsequent inertia once in flight combined with shape does lend itself to the equation, but not so much as to be an issue for a hand gun at close range. Were we discussing rifles at distance, I'd bias my view towards those being larger factors, but we're not.
The OP is finding that his hand gun is zero'd for a heavier, slower bullet, and when he fires a lighter faster bullet it's going high. Well, it's not going high, it's simply getting to the target before it's had a chance to drop as much as the slower round.
Look at the back of a box of ammo and see where the trajectory plot is. The only thing I have handy is some .40s&w and that has a zero of 25yds, and is -1.4" at 50. This means if the gun is zero'd for 25yds (75') with that ammo, and you shoot something at 25' (8.3yds) it will impact high.
Bullet mass and subsequent inertia once in flight combined with shape does lend itself to the equation, but not so much as to be an issue for a hand gun at close range. Were we discussing rifles at distance, I'd bias my view towards those being larger factors, but we're not.
The OP is finding that his hand gun is zero'd for a heavier, slower bullet, and when he fires a lighter faster bullet it's going high. Well, it's not going high, it's simply getting to the target before it's had a chance to drop as much as the slower round.
Look at the back of a box of ammo and see where the trajectory plot is. The only thing I have handy is some .40s&w and that has a zero of 25yds, and is -1.4" at 50. This means if the gun is zero'd for 25yds (75') with that ammo, and you shoot something at 25' (8.3yds) it will impact high.
Here is what I have experienced just this summer trying to come up with a 357 mag load.
Out of my Marlin 1894C with 18" barrel and close to max 357 handloads:
125gr JHP impacted aprox 6" higher than 158gr JHP at 50 yrds.
Out of my Ruger GP100 with 4" barrel, same loads:
125gr JHP impacted aprox 6" lower than 158gr JHP at 40 yrds.
So, at least for me, they were almost exactly backwards from each other.
Just info to think about. I dont pretend to know why.
VL
Out of my Marlin 1894C with 18" barrel and close to max 357 handloads:
125gr JHP impacted aprox 6" higher than 158gr JHP at 50 yrds.
Out of my Ruger GP100 with 4" barrel, same loads:
125gr JHP impacted aprox 6" lower than 158gr JHP at 40 yrds.
So, at least for me, they were almost exactly backwards from each other.
Just info to think about. I dont pretend to know why.
VL
If muzzle rise was attributable to this, then a bench rest rig would never fire straight.
Muzzle rise is attributable to the jet engine you produce when the bullet uncorks the barrel. Before that occurs the inertia of the slide retains everything in alignment, or else your shooting technique would need to anticipate the lift due to muzzle rise, and we all know that isn't the case.
Muzzle rise is attributable to the jet engine you produce when the bullet uncorks the barrel. Before that occurs the inertia of the slide retains everything in alignment, or else your shooting technique would need to anticipate the lift due to muzzle rise, and we all know that isn't the case.
Muzzle rise begins the instant the cartridge goes off
Long (in relative terms) before the bullet exits the muzzle. As soon as gas pressure builds up in the case, it pushes in all directions, equally. Pressure to the sides is held by the chamber walls. Pressure to the front is what pushes the bullet down the barrel. And pressure to the rear is transleted into force against the breechblock, which, being a fixed part of the gun (at this time) means the rearward force is transferred to the firearm, as a whole.
Muzzle rise occurs because we hold our guns below the line of the bore. Most pronounced with handguns, but it happens with rifles as well. Note how rifles with straight line stocks exibit the least muzzle rise. This is because the force is allowed to push strait back, instead of trying to rotate the gun around the pivot point created when the grip (or buttstock) is below the line of the bore.
This was figured out a long time ago, and is one of the factors involved in creating precise sights. The other major factor is gravity (bullet drop). The line of your sights (either iron or optical) is not parallel with the line of the bore. They are made to intersect, and the point where they do is where you are "sighted in" for.
This is an example of the main difference between rifles and handguns concerning muzzle rise, velocity, and drop. The rifle has a lot more mass, and the force of recoil acts on the buttstock, a much straighter line than the grip of a handgun. The effect of muzzle rise (before the bullet clears the muzzle) on the rifle is much less in the rifle than the pistol, even though the bullet spends slightly more time going down the barrel. The 125s are going faster than the 158, so their time of flight to the target is less than the 158s, and so, with less time for gravity to work its constant, the drop less, at the given range.
With the handgun, with its extreme leverage due to the angle of the grip in relation to the line of thrust from recoil, and the smaller mass, having less inertia to resist movement, muzzle rise is enough greater than what happens in the rifle, and is enough to have a noticable effect on the bullet, as it moves down the bore. Think energy over time. Heavier bullets, spending more time in the barrel than light bullets, the greater muzzle rise of the handgun has a much more noticable effect. Which is why lighter (faster) bullets hit lower (with the same sight setting) than heavier ones, they get out of the barrel sooner, before it has risen as much.
Long (in relative terms) before the bullet exits the muzzle. As soon as gas pressure builds up in the case, it pushes in all directions, equally. Pressure to the sides is held by the chamber walls. Pressure to the front is what pushes the bullet down the barrel. And pressure to the rear is transleted into force against the breechblock, which, being a fixed part of the gun (at this time) means the rearward force is transferred to the firearm, as a whole.
Muzzle rise occurs because we hold our guns below the line of the bore. Most pronounced with handguns, but it happens with rifles as well. Note how rifles with straight line stocks exibit the least muzzle rise. This is because the force is allowed to push strait back, instead of trying to rotate the gun around the pivot point created when the grip (or buttstock) is below the line of the bore.
This was figured out a long time ago, and is one of the factors involved in creating precise sights. The other major factor is gravity (bullet drop). The line of your sights (either iron or optical) is not parallel with the line of the bore. They are made to intersect, and the point where they do is where you are "sighted in" for.
This is an example of the main difference between rifles and handguns concerning muzzle rise, velocity, and drop. The rifle has a lot more mass, and the force of recoil acts on the buttstock, a much straighter line than the grip of a handgun. The effect of muzzle rise (before the bullet clears the muzzle) on the rifle is much less in the rifle than the pistol, even though the bullet spends slightly more time going down the barrel. The 125s are going faster than the 158, so their time of flight to the target is less than the 158s, and so, with less time for gravity to work its constant, the drop less, at the given range.
With the handgun, with its extreme leverage due to the angle of the grip in relation to the line of thrust from recoil, and the smaller mass, having less inertia to resist movement, muzzle rise is enough greater than what happens in the rifle, and is enough to have a noticable effect on the bullet, as it moves down the bore. Think energy over time. Heavier bullets, spending more time in the barrel than light bullets, the greater muzzle rise of the handgun has a much more noticable effect. Which is why lighter (faster) bullets hit lower (with the same sight setting) than heavier ones, they get out of the barrel sooner, before it has risen as much.
Muzzle rise due to the bullet still in the bore - I don't think so...
The bullet weighs 115+ grains, vs a gun that weighs some where around 2.5 pounds. The inertia of the gun is far in excess of the mass of the bullet, thus the bullet is forced from the bore rather than the gun being forced from the bullet (think about that). There's also the recoil buffer spring which is typically 10 pounds or better (mine are closer to 18). So you have 230 grain bullet pushing against a 3 lb gun being held in lock by a 18 pound spring. The bullet is out the bore before the uncorked gasses produce sufficient thrust to then unlock the slide.
Prior to the gasses being released, you only have the weight of the projectile as force against the frame and breech block. The gasses inside the chamber have no interaction on the world outside, and as such they produce no force to be compensated.
If what you propose is true, putting a bullet on target with a subcompact gun would be nearly impossible as the mass of the gun is much closer to that of the bullet and it surely would be flipping up uncontrollably long before the bullet cleared the barrel. The front sight post would also be unusually tall to ensure the muzzle aimed down enough to allow for appropriate rise as the bullet left the barrel.
The bullet weighs 115+ grains, vs a gun that weighs some where around 2.5 pounds. The inertia of the gun is far in excess of the mass of the bullet, thus the bullet is forced from the bore rather than the gun being forced from the bullet (think about that). There's also the recoil buffer spring which is typically 10 pounds or better (mine are closer to 18). So you have 230 grain bullet pushing against a 3 lb gun being held in lock by a 18 pound spring. The bullet is out the bore before the uncorked gasses produce sufficient thrust to then unlock the slide.
Prior to the gasses being released, you only have the weight of the projectile as force against the frame and breech block. The gasses inside the chamber have no interaction on the world outside, and as such they produce no force to be compensated.
If what you propose is true, putting a bullet on target with a subcompact gun would be nearly impossible as the mass of the gun is much closer to that of the bullet and it surely would be flipping up uncontrollably long before the bullet cleared the barrel. The front sight post would also be unusually tall to ensure the muzzle aimed down enough to allow for appropriate rise as the bullet left the barrel.
Everything you say is true but there is one oversimplification.
In a given caliber, a heavier bullet typically means lower velocity since it's not possible to push a heavy bullet as fast out of a given cartridge as it is possible to push a light bullet. That means that, practically speaking, velocity and bullet weight are connected so you can't really say that bullet velocity has nothing to do with bullet weight.
That's really neither here nor there because at the ranges we're discussing trajectory is pretty much a non-issue in comparing the impact points of various loads from a given pistol. There's also another factor, and that factor, not trajectory, is the one that dominates in handguns at close range. That factor is how much the muzzle rises in recoil before the bullet exits the barrel.
That's a good point. At this time, take a second to visit the S&W site and look at pictures of the 317 and the 360PD and tell me what difference you see in the height of the front sights. You'll notice that the .357Mag lightweight revolver has a much higher front sight to compensate for the much greater muzzle rise compared to the same weight gun in 17Magnum.
If you look closely you'll see that when the sights are lined up, the muzzle of the 360PD is pointed noticeably downward.
The slide begins to move backward as soon as the bullet starts to move. There are some videos below that prove it. The jet effect (gases escaping from the muzzle behind the bullet) is not required to unlock the slide, it is well on its way to unlocking before the jet effect even comes into play.
While it is true that the jet effect does contribute to recoil, it is the bullet's motion that contributes most.
Recoil, which produces muzzle rise, is a function of conservation of momentum. As soon as the bullet begins to move it has momentum and therefore as soon as the bullet starts to move the gun also begins to move in recoil. Anything else would violate the laws of physics. You are correct that the gun doesn't move a lot before the bullet exits the barrel but it doesn't have to. Just 1 millimeter of muzzle rise on a gun with a 6" barrel will raise the point of impact about 6" at 25 yards.
As a matter of fact, there is, in one sense, an anticipation of the muzzle rise. The sights anticipate the muzzle rise due to recoil. In fact, on a long barreled pistol it is often easy to see that lining up the sights will result in the bore being pointed noticeably downward. Here's one example courtesy of BillCA
and another off the web.
If you line up the top of the sights with one ruler and use a second ruler lined up to the barrel you will see that the two rulers diverge noticeably. That means that the barrel is obviously pointed downward when the sights are properly aligned for shooting.
For those who are still unconvinced, here's some undeniable proof. The video in the link below is a compilation of several slow-motion videos of firearms being shot. One segment of the video (from 2:13 to 2:37) shows an extreme slow motion closeup shot of the muzzle of a 1911 pistol. It is plainly obvious that the slide/barrel have started to move long before the bullet exits the barrel. There is noticeable movement for 8 or 9 frames of the video before the bullet is visible at the muzzle.
http://www.youtube.com/watch?v=kq-xcqs5NIk
In a normal situation (where the gun is not held firmly against a sturdy rest) that motion would also have involved a bit of muzzle lift.
Here's another one. Put it to full screen and stick a post-it note or a bit of tape on your monitor so that it is exactly touching the bottom of the barrel. Now play around with the video until you get it stopped at a point between the gun firing and the bullet exiting the barrel. Look at the barrel and you'll now see some space between the bottom of the barrel and your reference mark demonstrating conclusively that the muzzle has risen prior to the bullet's exit.
http://www.youtube.com/watch?v=BW93WQ98s-I
And another. If you look at these shotguns being fired, particularly starting about the 8 second mark you'll see that there's a considerable amount of recoil movement before the shot exits the barrel.
http://www.indyarocks.com/videos/Gun-Fire-Ultra-Slow-Motion-335584
I suppose it is, now and again, comforting to find proof that the laws of physics are still in effect.
CarterMccoy
New member
1911 Jim,
That was most likely the best, most scientific and colorful presentation of the material I have ever seen.
It is a pleasure to be in your company sir, you are a breath of (knowing what you are talking about) fresh air.
Doc.
"The gasses inside the chamber have no interaction on the world outside"
Thanks again 1911 Jim.
That was most likely the best, most scientific and colorful presentation of the material I have ever seen.
It is a pleasure to be in your company sir, you are a breath of (knowing what you are talking about) fresh air.
Doc.
"The gasses inside the chamber have no interaction on the world outside"
Thanks again 1911 Jim.