Bullet weight, velocity, and vertical POI

[Random 8]

This video is of a higher recoiling handgun that does not have muzzle rise mitigation devices. It is slowed down to appropriate speed to see the bullet as it leaves the muzzle. The rise in muzzle is appears very minimal at a glance, but think of the rise in terms of MOA and it is significant. Also think of it in terms of a force imparted to the bullet in the millisecond it is traveling the bore, and it is a significant acceleration.

 

[Atavar]

And yet again the muzzle rise does not start until *after* the bullet has left the barrel. Once the bullet leaves the barrel it doesn’t matter for this shot what the gun does.

 

[Pat Riot]

Did you have a chance to chronograph the results?

No, I do not have a chronograph.

 

[Pat Riot]

Thanks for running that test and reporting the results. I'm curious - was there a noticeable difference in recoil between the 205 grain loads and the 255 grain loads?

Oh yes, the 205 grain bullet loads were almost like shooting .38 Specials from my model 19. The 255 grain loads have a bit of recoil and flash. The thing that I like is both loads shoot very accurately from my S&W 25, Ruger Vaquero and Ruger New Vaquero.

 

[Random 8]

And yet again the muzzle rise does not start until *after* the bullet has left the barrel. Once the bullet leaves the barrel it doesn’t matter for this shot what the gun does.

If you're going to watch that ( to the end and the higher speed photography) and claim the muzzle rise doesn't start until after the bullet has left the barrel, I'm done here. Good luck.

 

[Pat Riot]

This video is of a higher recoiling handgun that does not have muzzle rise mitigation devices. It is slowed down to appropriate speed to see the bullet as it leaves the muzzle. The rise in muzzle is appears very minimal at a glance, but think of the rise in terms of MOA and it is significant. Also think of it in terms of a force imparted to the bullet in the millisecond it is traveling the bore, and it is a significant acceleration.

I can see the muzzle rise ever so slightly in that video just before the bullet is exiting the barrel looking at it on my iPhone. Cool video. Thank you.

 

[JohnKSa]

Even in your video though the bullet has left before the muzzle begins to rise. Look at 1:14 in the video you provided and the bullet is down range before the pistol starts to lift from the rest.

That is because the slide of the gun isn’t coupled tightly to the frame. So it recoils directly backwards instead of rising.

In a gun like a revolver where the barrel is fixed to the frame, the barrel begins to move the instant that the bullet does--just like in the gun with the slide/floating barrel. Since the barrel can't move without the frame moving, the whole gun moves. Since the restraining force applied to the gun by the shooter is below the bore axis, the movement will manifest in the form of muzzle rise. Therefore the muzzle rise in a gun like a revolver will begin the instant that the gun begins to move in recoil.

You can have all the slide motion you want but if the bullet is gone before the muzzle rises it is not going to affect poi.

Exactly correct. Go back and look at my post #16 on this thread--here's the important part.

Some semi-auto pistols are set up so the slide/barrel move straight backwards while the bullet is in the bore. In guns like that, there won't be much POI change from various loadings because during the time the bullet is in the bore the slide/barrel are pretty much only moving backwards--you get recoil, but the recoil isn't causing significant muzzle rise until the barrel & slide hit the frame and transfer momentum to the frame. In guns where the barrel is fixed to the frame (or some semi-autos with links where the barrel starts tilting almost immediately when the bullet starts moving) then recoil and muzzle rise happen together and you can see significant changes in POI due to different loads.

If what you are avowing were true the laser boresight would appear significantly lower than poa.

Correct. It will be in a centerfire revolver. You don’t even need a laser boresight to see the downward angle of the bore in some cases, you can just look at the gun and see that the bore is pointing downward with respect to the sights.

Take a look at the revolver in this article. Set a ruler across the top of the sights and you should be able to easily see that the bore is actually pointing downward with respect to the sights.
https://www.americanrifleman.org/content/a-lady-competitor-s-colt/

In reality the bore actually does effectively aim up with respect to the sight line.

It does not in a centerfire revolver at the moment of firing. I gave you a simple test you can perform to see that this is true so you don't have to take my word for it. The muzzle will indeed be pointing upward at the moment that the bullet leaves the bore due to muzzle rise, but at the moment that the gun is fired, it is actually pointing downward with respect to the sight line. Muzzle rise while the bullet is still in the bore will bring the bore up to provide the trajectory necessary to hit the target.

You can do the same test with the dowel and a yardstick on a semi-auto pistol with a floating barrel and see that things are quite different because of the fact that the slide and barrel recoil almost straight back and there’s no significant muzzle rise until they hit the frame.

 

[Atavar]

I hunted for many years with a .44 magnum revolver. My bore was aligned with the iron sights and it worked just fine. I brought home more than my share of deer with that revolver shooting 20 to 150 yards.
Talk to people shooting competitive pistol and ask them if they try to compensate for muzzle rise by aiming low. I am sure we have some competitive shooters here that can chime in.

 

[JohnKSa]

I hunted for many years with a .44 magnum revolver.

I shot a .357Magnum revolver for years and did quite well with it. But I never noticed that the bore was angled down with respect to the sights until I actually did the test I described.

My bore was aligned with the iron sights and it worked just fine.

You won't notice the misalignment until you actually do the test I gave you. I never did, then I did the test and it was very obvious.

Talk to people shooting competitive pistol and ask them if they try to compensate for muzzle rise by aiming low.

That's not what happens at all. When you zero the gun, you align the sights to compensate for the muzzle rise. Once the sights are set up so you hit the target where you're aiming, there's no need to do anything but aim at the target. The muzzle rise will bring the bore up to where it needs to be to hit where you're aiming. BUT, with a different loading that causes a different amount of muzzle rise before bullet exit, you will have to re-zero.

That's with a handgun that has a barrel fixed to the frame. If the gun is a semi-auto with a floating barrel, then the recoil motion of the slide/barrel while the bullet is in the bore is pretty much straight backwards so there's almost no muzzle rise and therefore no need for a downward angle to the bore.

Did you look at the revolver in the article I linked and set a ruler across the sights? It's pretty easy to tell that the bore is angled downward with respect to the sights

I used the test method I described some years back and made some diagrams from a few guns I had on hand.

https://thefiringline.com/forums/showpost.php?p=6459338&postcount=3

You can see that the angle of the revolver's bore was decidedly downward with respect to the sightline while the autopistols didn't show the same issue at all.

 

[Atavar]

That's with a handgun that has a barrel fixed to the frame. If the gun is a semi-auto with a floating barrel, then the recoil motion of the slide/barrel while the bullet is in the bore is pretty much straight backwards so there's almost no muzzle rise and therefore no need for a downward angle to the bore.

Did you look at the revolver in the article I linked and set a ruler across the sights? It's pretty easy to tell that the bore is angled downward with respect to the sights

I used the test method I described some years back and made some diagrams from a few guns I had on hand.

https://thefiringline.com/forums/showpost.php?p=6459338&postcount=3

You can see that the angle of the revolver's bore was decidedly downward with respect to the sightline while the autopistols didn't show the same issue at all.

I boresighted my .44 revolver with a laser to true the bore to the sights. I think that is a little more definitive than putting a wooden stick in the bore.
If what you are saying is true then every revolver made is designed for one particular cartridge and bullet and powder weight and will compensate correctly only for a specific bullet mass and velocity. That should be advertised to buyers when they purchase a revolver.

 

[JohnKSa]

Is it still zeroed? By that, I mean is it set up so that it will hit where the sights are aiming? If so, get it out, put the bore sighter in, and then aim at a point on the wall across the room. The dot from the boresighter will be significantly below the sights if it is still zeroed.

In post #26, there's a picture of a .357Mag being fired. If you hold a card to the bottom of the barrel during the 224,000fps section of the video you can clearly see that the muzzle is rising noticeably before the bullet leaves the bore.

Look at the revolver in the article I linked in post 32 and put a ruler across the sights. You should be able to very easily see that the bore angles downward with respect to the sights.

If what you are saying is true then every revolver made is designed for one particular cartridge and bullet and powder weight and will compensate correctly only for a specific bullet mass and velocity. That should be advertised to buyers when they purchase a revolver.

Well, if you are talking about fixed sight revolvers, there's some truth to this. Generally only a fairly narrow range of loadings will match up the POA/POI precisely. Loadings that produce more muzzle momentum will hit higher, loadings with less will hit lower on the target. If you read the forums very much, you will see people talking about using different loadings to try to get a fixed sight revolver to shoot to point of aim.

In revolvers with adjustable sights, you just adjust the sights for the load you want to shoot.

Ok, try this.

Look at 0:51 in the video from post #26. Watch for the flash at the muzzle and stop the video. Measure from the red play line to the bottom of the barrel lug. On my screen it's 2.9cm at the point when the flash is first visible.

Now let the video play until the bullet is just exiting the muzzle and pause again. That's about 0:55 in the video. Do the measurement again. On my screen it's now 3.2cm above the red play line. The muzzle rose 3mm on the screen between the time the first flash was visible at the muzzle and when the bullet exited.

You can measure again at 1:06. At that point there's just the beginning of the flash at the muzzle and the barrel lug is 5.3cm above the red play line on my screen. At 1:09, the bullet is just exiting and the barrel lug is now 5.6cm above the red play line on my screen. Again there's clearly been muzzle rise while the bullet was still in the bore.

If you want to really see a dramatic representation, pause at 1:06 where the flash is just barely showing. Line up one end of a ruler with the bottom of the barrel lug and place a sticky note on the screen at the other end of the ruler so that the bottom edge of the sticky note is perfectly aligned with the ruler which is aligned with the barrel lug.

Now advance the video to the point where the bullet is just exiting. Line up the ruler again with the bottom of the barrel lug and it will be immediately very obvious that the barrel lug is no longer aligned the way it was at the moment of firing because the ruler won't line up with the post it note any longer.

 

[Atavar]

Let’s say for discussions sake you convinced me. It is still moot with regards to the original question.
All you are saying is that revolvers are engineered to compensate for muzzle rise so the barrel will be level when the bullet exits.
From that point it is subject to the laws of physics and will drop at 32ft/s/s

 

[JohnKSa]

The original question was about "different bullet weights and/or velocity " having "sometimes radical effects on vertical POI". I think that explaining why that is true and the physics behind it is extremely relevant.

All you are saying is that revolvers are engineered to compensate for muzzle rise so the barrel will be level when the bullet exits.

I don't really think anybody sat down and engineered things in the sense that they did calculations to figure out the sight height based on the idea that the muzzle would rise before the bullet exited.

My guess is that they built prototypes and put sights on them that would get the guns shooting to point of aim. At least in the beginning.

Maybe somewhere along the way, someone actually figured out that the muzzles on fixed barrel handguns point significantly downward compared to the sights and then worked out the math to figure out how to compensate for it. I don't really know, but that seems hard compared to just putting a really tall front sight on the gun and filing it down until the gun hits where you want it to.

From that point it is subject to the laws of physics and will drop at 32ft/s/s

Well, it's not just subject to the laws of physics from that point--it is from the beginning. Everything is always subject to the laws of physics.

The reason that the muzzle rises in a fixed barrel handgun is physics.

Conservation of momentum (a principle of physics) is responsible for the force of recoil. The forces applied to the handgun by recoil and the shooter's hand result in the torque on the handgun since the hand providing the resistance to movement is below the barrel where the recoil is generated. It's all physics.

 

[Random 8]

Thank you @JohnKSa for having the time, patience and knowledge to delve into and explain this. I think you may have the data already from your measurements to come up with an approximation. My calculus is not so good in terms of raw numbers. My follow up question would be what is the effect of the vertical acceleration (above and beyond the physical height of the barrel on exit) imparted to the bullet during travel in the .357 mag example? Intuitively I believe it is significant at medium ranges.

 

[paul105]

A little late to the party, and I only skimmed the replies. The below target was shot rested at 25yds using a 4 1/4" S&W Model 69 (5 shot L Frame .44 Mag). POA for all loads was the big center diamond. Only shot two rounds to eliminate target clutter and minimize recoil induced fatigue.



Note the horizontal dispersion in addition the the intuitive vertical.

Paul

 

[JohnKSa]

My follow up question would be what is the effect of the vertical acceleration (above and beyond the physical height of the barrel on exit) imparted to the bullet during travel in the .357 mag example? Intuitively I believe it is significant at medium ranges.

It's just a gut feel, but I think the contribution due to the upward velocity of the muzzle is going to be pretty small. I figure it's definitely going to be less than the contribution of muzzle position since the magnitude tends to go down as you differentiate and velocity is the derivative of position. I don't really have a way to measure it. You would need extremely high-speed video and a controlled setup with a very closeup shot to measure the upward velocity of the barrel because the time interval is so short and the movement is so small.

 

[Leon tP]

A little late to the party, and I only skimmed the replies. The below target was shot rested at 25yds using a 4 1/4" S&W Model 69 (5 shot L Frame .44 Mag). POA for all loads was the big center diamond. Only shot two rounds to eliminate target clutter and minimize recoil induced fatigue.

View attachment 1058741

Note the horizontal dispersion in addition the the intuitive vertical.

Paul

There certainly seems to be a loose correlation between Power Factor and vertical shot placement.

Notice the 240's at the 3 O'clock position on the diamond. I see they're at 880 fps (211 PF).

Next there's the 240's, 250's and 260's all at higher velocities with PFs ranging from (285 to 317 PF) similarly clustered around each other near the 12 O'clock noon position on the diamond.

Then there's the heavy hitters, the 310's (353 PF) and the 325's (383 PF) both hitting high on the target.
Recoil making it effects known to the shooter.

Thanks for posting that, very informative.

 

[JohnKSa]

Power factor is a scaled version momentum--they're basically the same thing but with a scaling factor difference.

Momentum is mass x velocity, but in this discussion we really only need to do comparisons so we can calculate it as bullet weight x bullet velocity.

Power factor is bullet weight x bullet velocity divided by 1000.

 

[9x56MS]

The vertical movement is pure physics, the thing I have not been able to figure is why bullets of the same weight but different manufacturer will change poi sometimes radically.

 

[Atavar]

Aerodynamics, cog
A less aerodynamic bullet will slow more rapidly.
Center of gravity can change how the bullet responds to rifling, as can hardness.

 

[Random 8]

Center of gravity can change how the bullet responds to rifling, as can hardness.

I noticed this with my own testing with the 158s in the TC. The SWC design with a longer bearing surface and different profile was consistently left of the other 2 RN and 2 TC designs tested. All were BHN 12. All likely had different CGs also. The 125 tested with a shorter bearing surface and BHN 15 plus velocity on the 158s was shifted slightly left also.

This becomes very apparent with rifle work as the range increases to 100 or 200 yards. Different profiles at same weight and velocity will often shift laterally, often significantly.

 

[Leon tP]

CoG and "trueness" (symmetry). If the bullets wobble too much they will shift or fail to be very accurate. After all, you can CAD them perfectly on paper but mass producing them that way is a bit harder.
Sometimes you can have bullets with void spaces that just get through the manufacturing process.
Let's not get started on barrel whip/flexing/harmonics.

 

[Rodfac]

In a gun like a revolver where the barrel is fixed to the frame, the barrel begins to move the instant that the bullet

Absolutely, this has been known and reported on for over 100 yrs! For those who doubt re-read Hatcher, Whelen, Crossman, Keith, Askins, Jordan, Cooper, Skelton, McGivern et. al. The first three were Frankfort Arsenal military ballisticians. The rest were: knowledgeable "amateurs" with extensive LEO and Civilian competition experience. Rod