Recoil and Semi-Autos (and maybe Revolvers, too)...

[polyphemus]

In this closed firing position the barrel
is therefore situated not parallel with
the top of the frame and breech-slide, but
the axis of the closed barrel inclines forward
and downward at a considerable angle;
however, as both ends of the barrel are
firmly secured in this position, and as on
firing a shot the inertia of the heavy breechslide
and of the barrel delays the rearward
movement of these parts until after the bullet
has passed from the muzzle of the barrel,
the inclined position of the barrel does not
affect the accuracy of the arm.

This quote above is from John Browning's 1910 patent application.What I find
interesting there,is that he describes rearward movement delayed until after the bullet leaves the muzzle.However physics says that bullet and slide move at the same time up on firing.

 

[Limnophile]

JohnKSa,

in an autopistol, there's little or no significant muzzle rise until the bullet exits the barrel.

Interesting comparison of sight line and bore axis. A bullet must obviously be launched at a slight upward angle (assuming one is firing at a target situated horizontally from the shooter), as the bullet's trajectory will intersect the line of sight twice -- first as it is moving upward, then as it moves downward.

The downward orientation of the revolver bore axis demonstrates that recoil causes more pre-bullet-exit muzzle rise than what is caused in a semiauto, but I assume that some such muzzle rise occurs in semiautos, too, if it is true that heavier bullets fired from them impact higher than lighter bullets.

 

[Walt Sherrill]

As I was struggling with all of this, I was perplexed about a couple of issues. Still am.

1) I don't see how a revolver's use of recoil (barrel rise, etc.) can be the same as semi-auto. Both weapon types MUST be affected and have barrel rise, but there OUGHT to be a noticeable difference. I noticed in a Starline Brass video that those folks, seemingly expert, seem to same the two weapons are affected in the same way -- but they don't directly say they are affected.

I also don't understand how barrel length affects recoil (as it, in turn, affects point of impact. (I do know that powder can be changed to ignite more quickly -- typical .22 WMR rounds designed for long guns and fired in a revolver or semi-auto perform differently than then using .22 WMR rounds designed for shorter barrels: less of the powder ignites OUTSIDE the barrel (i.e., less is wasted) when its matched to the barrel length. Barrel length and a given load could, and in theory, that would take longer and force the bullet to travel a greater as distance as recoil raises the barrel higher. But, barrel length could also allow more powder to be burned, which could, in turn, incease the bullet's velocity and speed the bullet down the barrel, shortening the time needed for it to exit. Same load but different performance. Too damned many variables.

2) Others tell us that most semi-autos, with an action design that delays recoil somewhat, there is can be a VERY SMALL amount of vertical movement during the early part of recoil. Most of the recoil-induced barrel movement isn't seen until the heavy barrel and slide slam back against the frame (stop area) and causes the assembly to tilt. With a semi-auto there is an extra step in the recoil process, evidenced in the entire barrel and slide moving to the rear before the bullet exits the barrel. But it happens quickly -- with the barrel moving to the rear by about 1/10th of an inch before the bullet is gone. That amount of movement, pressing against a spring that will apply only trivial amounts of force against the frame, and will generally apply it BELOW the bore axis (but above the hand holding the gun) -- its still there, but argulably with less effect.

3) The later effects of recoil can be somewhat less obvious in a semi-auto than when using similar loads in a revolver. -- both because there is higher bore axis in the revolver and nothing DELAYING or redirecting the force of bullet's movement as in semi-autos. In either type of weapon, some work is being done BEFORE the bullet leaves the barrel, so there should be evidence of that work being done -- if not VISIBLE muzzle rise, at least with a visible change in points of impact. Bore axis complicates the comparison. Then, too, some revolver designs have a very low bore axis (ala the Mateba design, with the barrel aligned with the bottom of the cylinder.) I wonder how muzzle rise affects point of impact with a low-bore axis revolver compared to one with a high bore axis.

If we could perform the same test in a Ransom Rest, one series of shots done normally, and another series done with the slide locked, we might see some interesting differences. I'd like to see Ransom Rest tests of semi-autos with similar barrel lenghts firing similar loads, too. Nobody, thus far has done that to addressed any of these "difference" question, showing us evidence with aimed targets shot from a rest. I'd really like to see that.

4) Revolvers are a little different, if only because of bore axis. Some also say that revolver recoil has two phases -- one in the cylinder, and a second when the round is in the barrel. I don't know that recoil in revolvers is a two phase process -- as, to me, it just seem like a slight reduction of the forces put into effect the primer is ignited and the bullet passes the cylinder gap. All we're really concerned about is the bullet's velocity as it leaves the barrel and the angle of the barrel if it's affected by recoil. The gases lost in the barrel/cylinder gap might be the equivalent of work done like gases transferred via a gas piston in a semi-auto that uses gas pressure to cycle the action. The gap is also (in terms of force redirected) a bit like a compensator, but it's doing its job a bit earlier in the bullet's travel.

As for the sight alignment in revolver and their higher front sights -- sometimes offered as evidence of a revolvers innate tendency to shoot higher than a semi-auto: it is different, but some part of that height is necessary because the rear of most revolvers becomes increasingly BEEFY as calibers go up -- as extra material is needed in the cylinder and the frame to keep things together. That extra material raises the rear sight, and the front sight has to be raised, too.

5) What seems to be a confusing factor in this discussion is that a number of bullets are aerodynamically different, and because we're not shooting our weapons in a vacuum that difference may be greater than we might expect. Limnophile gave us an example of 9x18 rounds that seemed identical, but performed differently -- and bullet structure seemed to be the difference.

I found PMC .357 magnum loads (C and F in the chart below) where the heavier round (158 gr) and the lighter round (125 gr) had the same muzzle velocity (1194), but the 125 gr. round hit at .62" above level at 25 yds, while the 158 gr round hit at .61" (i.e., lower) at the same distance. The heavier bullet dropped less than the lighter one at all measured distances which is NOT the normal performance of heavier bullets with similar or lower velocity.. The bullet designs are quite different, the aerodynamics of the rounds might be the cause. Here's a base of PMC data that gives performance at distances.

It's hard to find comparison data for round performance. In the chart above, things are GENERALLY as theory says they should be -- except that round F, mentioned earlier doesn't behave in the expected manner when compared to round C. (The unexpected performance may be explained by inertia, and the heavier bullet's better aerodynamics), with the resistance of the air having less effect on the heavier and more aerodynamic round.) It's obvious I'm not as familiar with the PHYSICS involved in this discussion as some.

I have yet to find a high-speed video of a revolver that clearly shows the barrel position as the bullet leaves the barrel, and soon after. Nor have I found a video showing how a semi-auto's recoil and assumed muzzle rise, when the delay is removed) is different: there ought to be a different point of impact. And bore axis shouldn't be a big factor as the bullet leaves the barrel.

Ransom Rest tests addressing any of these unanswered questions or issues would be helpful; that would require that someone align the sights with each shot -- typically NOT the way Ransom Rest tests are done. For at least one of the tests, you'd probably have to be able to lock the semi-auto's slide, and that's not easy with all semi-autos. (Revolvers with 4" and 5" barrels can be found that shoot 9mm and 40mm and 10mm and .45 ACP rounds. I'd like to see the performance of those rounds differ, if at all, with all using the same loads (and barrel lengths).

 

[Walt Sherrill]

What I find interesting there, is that he describes rearward movement delayed until after the bullet leaves the muzzle.However physics says that bullet and slide move at the same time up on firing.

Delayed shouldn't be read as "stopped". It might be better understood as "slowed" as barrel and slide movement starts immediately and isn't interrupted. Some part of the force of the recoil is redirected (into the recoil spring almost immediately. How much force is transferred in that first 1/10th of an inch or more is hard to assess, but could probably be measured in some way. Beyond that point the bullet is gone, and part of the slide's momentum are also passed into the recoil spring -- but not all.

I know that you can shoot a semi-auto without the recoil spring without really damaging it. I wonder how the point of impact is affected, when the spring isn't there in the early phase to slow the barrel and slide movement, so that things happen sooner. Because the bullet leaves so quickly, it should have only a little effect there, but because there is no recoil spring the difference should be more visibile.

 

[polyphemus]

Slow down is definitely better than than hold up,I still have trouble with that
because the slide needs all the recoil energy it can get to complete the cycle and slowing it down must of necessity dissipate energy.

Departure of the bullet drops the pressure in the barrel established in the initial portion of the firing phase (i. e., when the bullet was still in the barrel as shown in fig. 29) to zero. Seen from the viewpoint of effect on the pistol,this imparts a rearward force on the slide assembly (see arrow in illustration) equal to the inertia of the departing bullet.

This from Kuhnhausen's shop manual.
The way I read this then,the effect of the pressure drop to zero is to impart a
rearward force to the slide and I find that hard to believe.

 

[Limnophile]

Walt,

Limnophile gave us an example of 9x18 rounds that seemed identical, but performed differently -- and bullet structure seemed to be the difference.

I must not have been clear. The comparison to which you refer is between a 9x18 95-gr RN FMJ and a 9x19 147-gr FN FMJ.

The ballistic coefficient is a bullet's mass divided by the product of cross-sectional area and an aerodynamic drag coefficient. The 95-gr 9 Makarov has a more streamlined nose, but it is a bit wider (0.363 in vs 0.355 in), shorter, and, of course, a lot lighter. As I recall, longer bullets tend to be more aerodynamic. The 147-gr 9 Luger, despite its nonaerodynamic flat nose, has a much greater ballistic coefficient due to its greater mass, slimmer profile, and greater length.

Thus, the two rounds exit the muzzle at the same speed, but the lighter, chubby, and short 9x18 decelerates faster than the 9x19.

Regarding your .357 Magnum example, it appears that the 158-gr SP has a higher ballistic coefficient than the 125-gr JHP. This is not surprising, because both bullets have the same cross-sectional area, the SP has a greater mass, and the SP must be longer. Thus, the heavier bullet is more aerodynamic and decelerates more slowly; thus, its trajectory is a bit flatter.

 

[Walt Sherrill]

Limnophile gave us an example of 9x18 rounds that seemed identical, but performed differently -- and bullet structure seemed to be the difference.

I must not have been clear. The comparison to which you refer is between a 9x18 95-gr RN FMJ and a 9x19 147-gr FN FMJ.

The ballistic coefficient is a bullet's mass divided by the product of cross-sectional area and an aerodynamic drag coefficient. The 95-gr 9 Makarov has a more streamlined nose, but it is a bit wider (0.363 in vs 0.355 in), shorter, and, of course, a lot lighter. As I recall, longer bullets tend to be more aerodynamic. The 147-gr 9 Luger, despite its nonaerodynamic flat nose, has a much greater ballistic coefficient due to its greater mass, slimmer profile, and greater length.

Thus, the two rounds exit the muzzle at the same speed, but the lighter, chubby, and short 9x18 decelerates faster than the 9x19.

Regarding your .357 Magnum example, it appears that the 158-gr SP has a higher ballistic coefficient than the 125-gr JHP. This is not surprising, because both bullets have the same cross-sectional area, the SP has a greater mass, and the SP must be longer. Thus, the heavier bullet is more aerodynamic and decelerates more slowly; thus, its trajectory is a bit flatter.

You were clear, and I just unintentinally messed up what you wrote. (I had just finished reading tables that showed rounds with similar design and weights that performed differently, and that apparently stuck in my mind as I was keying my comments.) I had read your post earlier, and understood what you entered but mangled things when I was trying to make a similar point. Your point was that the FMJ 9x18 round was an aerodynamically less efficient round than the slightly larger, heavier, longer-bodied flat-nosed 147 gr. 9x19 JSP round. The facts I presented, supposedly quoting you, didn't seem to make that point. I inferred (perhaps incorrectly) the same sort reasons for the performance difference you addressed when I compared the 124 gr JHP .357 to the 158 gr JSP .357 round. I say inferred as I have no experience with the JSP round -- and have only seen images of both.

I don't like making errors, but I like even less making errors and attributing them to somebody else. My apologies.

 

[Walt Sherrill]

Slow down is definitely better than than hold up,I still have trouble with that because the slide needs all the recoil energy it can get to complete the cycle and slowing it down must of necessity dissipate energy.

I think the biggest problem is simply storing enough energy to load the next round. The SLIDE will stop. It can only stop. Where else will it go? (If you fired the gun without a recoil spring, it would still stop, too -- and your gun will arguably not experience any damage. People on this forum who have done this say they don't feel a big difference in the recoil. The next round would NOT be loaded, however. (The recoil spring isn't there to stop the slide; it's there to load the next round.)

The energy created by the powder explosion doesn't happen immediately or instantaneously; the powder nearest the primer goes first and other powder is still igniting as the round goes down the barrel. Its very, very fast, to be sure, but so is slide and barrel movement (slower and in the other direction). In some cases, the powder may still be igniting/burning in the air after the round is gone. You can see this with many short-barreled guns -- that's big flame is powder that is ignited as the bullet leaves the barrel but doesn't add much to the bullet's motion/velocity.

Unless the round misfires, or the recoil spring is far too heavy for the round being fired, there is typically more than enough energy available to cycle the slide. Only a portion of the explosive force is stored in the recoil spring. A substantial part pushes the bullet out of the barrel, and a lot of it -- going in the other direction -- passes through the frame to your hands and arms, etc.

 

[polyphemus]

I think the biggest problem is simply storing enough energy to load the next round.

There's also a minor detail,cocking the hammer.
Anyway,M1911's are short recoil operated pistols and what that means is,recoil
force is only applied for a very short time, the rest of the rearward travel is
provided by the momentum in the slide,so we have powder ignition,case obturation,bullet and slide motion in opposite directions at the same time and
as the bullet exits and the barrel drops the slide continues on its own.
No delays in this process,elegant,simple and it works.

 

[JohnKSa]

What I find interesting there,is that he describes rearward movement delayed until after the bullet leaves the muzzle.

That is interesting. It's hard to know if he's saying that the rearward movement is delayed sufficiently that the barrel doesn't unlock before the bullet exits or if he really means it doesn't move at all before it exits. I'd like to think that it was the former as a little thought will tell a person that once the bullet leaves the barrel it no longer exerts any recoil force on the gun and therefore if the gun isn't moving by that point it won't move.

...if it is true that heavier bullets fired from them impact higher than lighter bullets.

I'm not sure that it is true. I haven't noticed any significant difference in the semi-auto shooting I've done. However, I wasn't really paying that close attention.

I have three boxes of 9mm ammo waiting for a chance to get to the range and do some testing. They're all the same brand but in three different bullet weights. I'll shoot them from the same locked breech gun at the same distances and see if there's a difference in POI. I'd like to do the same tests from a revolver and a blowback auto but that won't all happen in the same range trip.

...there is can be a VERY SMALL amount of vertical movement during the early part of recoil.

This is correct. The force of cocking the hammer (in hammer designs) and the loose coupling of the slide/barrel to the frame by the recoil spring should induce a small amount of muzzle rise. It's clear from the diagrams that the amount of muzzle rise is much, much smaller in a semi-auto than in a revolver.

The way I read this then,the effect of the pressure drop to zero is to impart a
rearward force to the slide and I find that hard to believe.

If I understand correctly, he's talking about the jet effect of the gases that escape forward out of the barrel once the bullet exits. Since the escaping gases are part of the ejecta, they do, indeed, account for some of the recoil force, but the vast majority is due to bullet momentum.

We're talking about the bullet momentum here and ignoring the gases, but in actuality, the recoil momentum is a function of the ejecta momentum, not just the bullet momentum. The ejecta is everything that comes out of the muzzle of the gun upon firing and that includes gases and some unburned powder.

 

[polyphemus]

That is interesting. It's hard to know if he's saying that the rearward movement is delayed sufficiently that the barrel doesn't unlock before the bullet exits or if he really means it doesn't move at all before it exits. I'd like to think that it was the former as a little thought will tell a person that once the bullet leaves the barrel it no longer exerts any recoil force on the gun and therefore if the gun isn't moving by that point it won't move.

Exactly so,barrel and slide are only locked while the bullet is in the barrel because the bullet is dragging the barrel forward and the slide is moving toward the rear, once the bullet's out the barrel can be easily pulled down by
the link and the case no longer pushes the slide back.Recoil force is only in effect while the bullet is in the barrel after that it's all momentum.

 

[Walt Sherrill]

There's also a minor detail,cocking the hammer.

Anyway,M1911's are short recoil operated pistols and what that means is,recoil force is only applied for a very short time, the rest of the rearward travel is provided by the momentum in the slide,so we have powder gnition,case obturation,bullet and slide motion in opposite directions at the same time and as the bullet exits and the barrel drops the slide continues on its own. No delays in this process,elegant,simple and it works.

We seem to be talking past each other. I think the following restatement is technically correct, but I'm sure somebody will correct the errors if it's not.

Recoil is what causes the momentum you describe. It all happens very quickly, to be sure -- but it's not an instantaneous event. Explosions are fast, but the force created is experienced over a longer period.

The delay we're talking about is not really a delay in the creation of the forces that cause recoil, but a delay in the way the force is transferred to the gun's frame.

Until the barrel is pulled down away from the slide, things are moving in a single plane -- bullet forward and slide/barrel to the rear. The bullet, however, leaves the barrel very quickly, and when i does the pressure that started things moving in both directions begins to drop. But, momentum has already been created by the force of the powder explosion, and that momentum pushes the slide and barrel to the rear. Those two pieces then separate. They both take a slightly different path but take their momentum with them. They are like a weight on end of a stick in your hand.

This discussion has been all about how much that delay affects (or delays) the barrel's rise from recoil. It doesn't have to be much to cause a noticeably big effect on the bullet's point of impact.

The bullet is gone from a 1911 before the barrel and slide have moved a tenth of an inch. The barrel doesn't rise noticeably at that point, but it may have risen enough to affect where the bullet hits a target. And we still have mostly theoretical answers in this discussion -- most of which make sense, regardless of the side of the argument you find most sensible.

The gun will fire without a recoil spring -- and it will do everything needed to function (including cocking the hammer or charging the striker) except chamber the next round. It needs the recoil spring's stored power to do that. The amount of force/energy/power stored in the recoil spring is a small fraction of the force that was generated by the bullet when fired. It's also not needed to stop the frame or charge the different springs. You can do this all of this by hand when you load the gun or hand cycle it -- so you know that it doesn't take a lot of force/energy to do those things.

Anything else experienced as a result of the slide and barrel's momentum -- the equal and opposite response to the bullet going in the other direction -- that is not stored in the recoil spring comes through the frame and into your hands, and into your body. Good technique, a well-designed gun grip, and a low bore-axis can make it very manageable.

 

[Walt Sherrill]

I have three boxes of 9mm ammo waiting for a chance to get to the range and do some testing. They're all the same brand but in three different bullet weights. I'll shoot them from the same locked breech gun at the same distances and see if there's a difference in POI. I'd like to do the same tests from a revolver and a blowback auto but that won't all happen in the same range trip.

I've found that you need to know at what distance the ammo was loaded to make point of aim and point of impact coincide. (some do 25 yards, some do 50 yards!!) I've discovered that not all ammo makers do it the same. That may throw off your comparisons. 50 yards was the sweet spot for the PMC ammo I showed earlier. Ammo set for 50 yards will perform differently than ammo set for 25 yards, and vis versa. Who woulda thunk that was an issue.

 

[JohnKSa]

I've found that you need to know at what distance the ammo was loaded to make point of aim and point of impact coincide.

It won't matter. If there's a difference in the POI due to muzzle rise it will show up on the target if all the ammo is shot from the same gun with the same sight setting at the same range and using the same POA. Short of loading all the different bullet weights to insure that all the loadings provide exactly the same muzzle momentum, there's nothing the ammo manufacturer can do to change that fact.

 

[Walt Sherrill]

It won't matter. If there's a difference in the POI due to muzzle rise it will show up on the target if all the ammo is shot from the same gun with the same sight setting at the same range and using the same POA. Short of loading all the different bullet weights to insure that all the loadings provide exactly the same muzzle momentum, there's nothing the ammo manufacturer can do to change that fact.

Perhaps. And maybe I'm misunderstanding the tables I've been looking at. (That sort of misunderstanding on my part is sometimes obvious in these discussions.)

The problem, as I understand it, is that if there is a difference in ammo performance due to the maker's design intent, unless unless you know that intent, you won't know for sure whether the differences you see are purely due to the difference in bullet weight, or whether the load is intended to have a POA/POI coincidence at a different distance.

The example cited earlier, of a 125 gr. PMC round that had a muzzle velocity of 1194 fps, and a 158 gr. PMC round that had muzzle velocity of 1194, but the the 25 yd POI was only .01" different, with the heavier round hitting lower, while the 50" POI was the same, and the 75 and 100 yd POI's were higher for the heavier round. You probably can't see the difference at 25 yards in that test. Same point of aim would give virtually the same results. In that case, it seems that the heavier round was more aerodynamically efficient.​

That example was really puzzling for me, at first -- and there are others just as puzzling when you compare rounds of similar size, weight (such as 9mm and .38 super) and similar (but exactly the same) velocities.

Factory rounds set to have POA/POI occur at 25yds will be dead on at 25, but low at 50. PMC and SPEER, for example are 50 yd ammos; those rounds will be as much as an inch high at 25 yds regardless of bullet weight. While Federal and some others are set for 25 yds.) I have the Hornady tables in front of me, and they seem to focus on 50 yds. Hornady shows trajectory tables for their rifle rounds, starting at 50 yds -- but not for their handgun ammo. It may be mostly velocity-related, but even so, if you're not chronographing your rounds, you might not be fully aware of the reasons for differences that show up.

 

[45_auto]

JohnKSa, per posts #39 and #40:

1911 Sight Axis and Bore Axis Relative to slide rails, from drawings here:

http://brlcad.org/design/drafting/M1911-A1_REDUX.pdf

It appears that I did mis-remember the angles slightly, it's been several years since I looked at them. Sight line DROPS 1 degree relative to slide rails, bore axis DROPS 0.9 degrees relative to slide rails.

This means that the bore axis actually RISES 0.1 degrees relative to the sight line, which means that if these drawings are correct that the bore is pointing about 2 inches above the POA at 25 yards.

Considering nominal machining tolerances, the sight line and bore line are essentially parallel, which implies that the muzzle of a 1911 does not experience significant upward movement during the time that the bullet is in the barrel.

I'll measure the sights of a few of my 1911's that I know shoot to POA at 25 yards tonight and see if their sights confirm what's on the drawings.

Top of rear sight:

Datum B to bottom of slot = .828
Datum B to bottom of slide = .118
Rear sight = .245
Height above slide surface = .828 + .118 + .245 = 1.191

Top of front sight:

Center of radius to top of sight = .102 - .087 = .015
Datum A to center of radius = .563
Datum A to Datum B = .378
Datum B to bottom of slide = .118
Height above slide surface = .015 + .563 + .378 + .118 = 1.074

Distance between Front and Rear sights:

Back edge of rear sight (tallest edge) from center = .3465/2 + .030/2 = .188
Tallest edge of front sight = center of radius
Center of rear sight cut to breech face = 1.782 + .103/2 = 1.833
Breech face to front of slide = 4.89
Front of slide to center of front sight radius = .270
Distance between high points of sights = 4.89 - .270 + 1.833 + .188 = 6.641

Point Of Aim (POA) relative to slide rails = Tan(-1) ((1.191 – 1.074) / 6.641) = 1.009 degrees DOWN

Barrel Bore Axis:

Front of barrel = thickness of bushing below slide bore = (.696 - .581) / 2 = .057
Back of barrel = flush with slide bore at front face of ejection port
Distance between front of barrel bushing and front face of ejection port = .091 + 4.89 – 1.3 = 3.681

Bore axis relative to slide rails = Tan(-1)(.057 / 3.681) = .887 degrees DOWN

Bore axis relative to sight axis = 1.009 - .887 = .122 degrees UP

POA at 25 yards is Tan(1.009) x 900 = 15.85 inches below slide rail
Barrel axis at 25 yards is Tan(.887) x 900 = 13.93 inches below slide rail

Barrel axis at 25 yards is 15.85 – 13.93 = 1.92 inches ABOVE Point Of Aim

Sight height above bore = .563 + .015 = .578

 

[JeffK]

Forgive me if this was linked somewhere, but does someone have real data showing a bullet rising above the barrel axis after it leaves the barrel? I'm skeptical of claims I read that heavy bullets hit high and light bullets hit low, from the same gun and aim point, assuming the heavy bullet is slower and ignoring recoil. Sophomore physics suggests the opposite would be true.

Long-range snipers talk about spin drift and the magnus effect, but this won't be significant for handgun shooting. Air resistance will affect faster bullets more, but this force is in the direction of travel, which is horizontal and not up/down.

If this is supported by real data, then it kinda has to be a recoil effect (rise of the barrel before the bullet leaves the barrel) because there's nothing left to explain it. In that case, firing guns from a vice should make the effect disappear, which would again be a nice observation if supported by real data.

There's a pile of misinformation out there on the net about rising bullets, but in every case I've found it's a misunderstanding due to the fact that the barrel is pointed slightly upward. I don't see any data showing a bullet rising above the barrel axis. I've never systematically tried to see a heavy bullet/light bullet difference myself at the range, but I've never noticed a difference either at least out to 25 yards with iron sights.

 

[David R]

This is what I have

I fired these rounds for other reasons. I always get targets like this with different weight bullets.

I had a Dan Wesson model 14 that only shot 105 grain bullets to point of aim. They shot much lower than all the other heavier stuff.

This is my Smith 637. Both loads are +P. Velocity is different for each load. Its 7 yards so BC makes no diff.

Its all I got today.

I think if the hand gun was held firmly so it would not move at all, the heavier would shoot lower. Just my opinion.


David

 

[44 AMP]

Factory rounds set to have POA/POI occur at 25yds will be dead on at 25, but low at 50.

I think you are getting a little confused here.

There is no ammo made with a "set POA/POI". There can't be! Ammo has a certain velocity and trajectory (varying with the barrel it is fired from).

POA/POI is the relationship between YOUR GUN and its sights (and how you look through them) with the ammo and where it hits on the target, relative to where you aimed.

Ammo makers cannot make a 25yd load or a 50yd load they make a load, and where it hits for you is where it hits for you.

The gun maker can "regulate" the sights for a given bullet weight at a given speed for a given distance. The ammo maker cannot.

And, remember that ALL loads trajectories are curves, like a rainbow. EVERY load can only be perfectly matched to the sights at only one distance, and will shoot above or below that an any other distance.

Lets take that 9mm 124gr@1200fps (or any other speed, including the original 9mm load a 124gr@1050fps) for example. IF the maker regulates the gun's fixed sights (meaning builds them that way) so the bullet hits "on" at 25yds, it HAS to be lower at 50yds with the same sight setting. Likewise the reverse, if factory "zero" is 50, it has to be high at 25.

ALL guns and every load does this, which is why adjustable sights are so handy when you want/need to match the sight POA with the bullet POI at varying distances.

Ammo is always the same, meaning a given load is always what it is, it is the different guns, their sights, and how we look through them that makes changes in POA/POI.

The gas in your car's engine doesn't affect where the car goes when you turn the steering wheel. (not a perfect comparison, but close enough I think)

 

[Limnophile]

David,

Finally, some empirical data.

I scored the height above the center of the bullseye of each shot, in bullseye radii, then entered the scores into an online unpaired t-test calculator. The height of the 158-gr round is statistically highly significantly higher than that of the 110-gr round (p < 0.01).

I'm now convinced that the phenomenon being discussed herein is real. Thanks.