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

[Walt Sherrill]

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).

They can control their test barrels, angle, etc. Your point is that that THAT their variables do not apply to your weapon and what you and JohnKSa are saying is that those ammo maker choices don't matter. I understand and stand corrected -- thanks to both of you for finally driving THAT point home. That shows how I misunderstood/misinterpreted what I was seeing. I just didn't follow the reasoning associated with what I was seeing far enough.

The test barrels and setting may be different from one ammo maker to another, and they may use different variables to get their data for the 25 yrd or 50 yard POA/POI coincidence, but that has no effect when the round is fired in your own weapon. I see. The ballistic curve is set for that load.

VELOCITY, WEIGHT and the bullet's areodynamic efficiency can account for the differences. Whether the test data is focused on 25 yards or 50 yards is arbitrary. But having some handle on those other variables might be useful. As noted in some of the results I posted there can be a number of exceptions to the "rules."

How do we ever show that a semi-auto with a short-recoil, locked-breech design performs differently than a revolver or a semi-auto with the slide locked -- in terms of how recoil affects barrel rise before the bullet leaves the barrel? That is what triggered this whole discussion.

The round will generally have the same ballistic curve regardless of the gun its in, but the curve may pass different points in space (have a different tilt, so to speak) depending on whether the gun is a semi-auto, a locked slide, or a is a revolver, etc.

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.

I understand your point. It all depends on the sight alignment for that particular load.

I think I understand Limnophile's point below, too. I read that as I was making a clarifying edit to this response.

 

[Limnophile]

44 AMP,

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.

On a curved trajectory there will be two distances at which POI = POA -- the first where the bullet intersects the line of sight on its upward leg; the second where the bullet intersects the line of sight on its downward leg.

One could arrange one's sights so that there is only one distance at which the bullet's path intersects the line of sight, but in that case the bullet will be below the line of sight at all other distances except for the distance at which the gun is sighted in at. This would be an inefficient sight arrangement, as it would maximize bullet drop relative to the line of sight beyond the sighted-in distance.

In big game hunting a common practice is to zero one's rifle at a distance where the maximum bullet rise between that distance and the shooter is no more than 3 inches. As I recall, that distance was around 200 yd for my .270 Win. The distance beyond that zeroed-in distance at which the bullet drops 3 in below the line of sight is known as the point-blank range, because there is no need to compensate for elevation out to that range (which I seem to recall is about 250 yd for the .270 with the round I was hunting with).

Using the ballistics calculator at handloads.com (which my Kindle Fire no longer functions with), and inputting the height of my sights above the bore axis on my CZs and assuming POA = POI at 27 yd (25 m), I believe the bullet trajectories first crossed the line of sight somewhere between 5 and 10 yd. As I recall, the maximum bullet rise between 10 and 27 yd was rather minimal, about 1 in.

 

[Walt Sherrill]

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.

I don't think anyone is claiming that the bullet is rising above the barrel axis after it leaves the barrel. Your sophomore physics is probably not at risk.

It's been a confusing discussion due to the many variables being addressed and further complicated (with time wasted) by at least one very obvious misunderstanding (mine).

Some here ARE asking how the bore axis (it's angle) is affected by the speed or weight of the bullet The argument is that recoil raises bore axis angle more when a heavier bullet is used. That's because that heavier bullet it is typically moving through the barrel more slowly and the gun's recoil has more effect. (What happens after the bullet has left the barrel is a different can of worms.)

We're also addressing whether the bore axis is affected differently by the bullet's travel in the barrel when the weapon is 1) a revolver, 2) a semi-auto, or 3) a semi-auto with the slide locked so that the action functions more like a revolver.

Some here believe that a semi-auto's bore axis angle change (rise) is delayed because the barrel and slide move to the rear before the slide slams back against the frame. A revolver doesn't have that same delay -- the barrel and frame are a single unit and move together. And because the bore axis of revolvers can be quite high, the effect (like a lever) can be more dramatic. What confuses things is that the bullet leaves the barrel very quickly -- before the slide and barrel of a semi-auto has moved to the rear more than a fraction of an inch. The semi-auto typically has a much lower bore axis.

If the bore axis angle is changed by the round being fired -- then the ballistic curve the bullet takes stays the same, but it starts and ends at different points, just as it does when you change your point of aim.

 

[Limnophile]

Walt,

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

No need to fall on your sword. This is an interesting thread -- I'm learning a lot; and, you're an interesting guy to have discussions with.

There seems to be a consensus about the cause of heavy bullets impacting higher than light bullets being the slower velocity of the heavy bullet resulting in a longer residence time in the barrel, thus being affected more by muzzle rise due to recoil. Consider that the heavy bullet imparts more recoil momentum and energy to the handgun, which itself should cause more of a muzzle rise, regardless of barrel residence time.

Take two Federal American Eage 9 Luger FMJs: the 115-gr RN and the 147-gr FN. The first has a muzzle velocity of 1,180 ft/s, the second 1,000 ft/s. The muzzle momentum of the two is, respectively, 19.4 and 21.0 ft·lb/s. The bullet muzzle momentum is conserved and imparted on the handgun. Using the empty weight of a CZ 75 Compact for the calculations, the free recoil energy of the two rounds is, respectively, 3.3 and 3.7 ft·lb.

Thus, the 147-gr round produces 8% more recoil momentum and 12% more recoil energy. I'm assuming more recoil must mean more muzzle rise, even while it is not perceptible to the eye.

I've read that some combat gamers prefer using 147-gr rounds because the recoil feels softer, because the slower moving bullet spreads the recoil momentum out over a longer time. I find that hard to believe, but if the phenomenon of heavy bullets impacting higher is due more to longer barrel residence time than to the greater recoil momentum, I suppose they could be right.

We need someone to calculate relative residence times for a nominal 4-in barrel to see what the difference is. One complicating factor is that muzzle velocities are actually velocities measured 10-yd (or is it 10-ft?) downrange. I doubt that gives a good approximation of true muzzle velocity.

 

[Walt Sherrill]

I've read that some combat gamers prefer using 147-gr rounds because the recoil feels softer, because the slower moving bullet spreads the recoil momentum out over a longer time. I find that hard to believe, but if the phenomenon of heavy bullets impacting higher is due more to longer barrel residence time than to the greater recoil momentum, I suppose they could be right.

I had that experience recently, firing 147 gr. rounds for the first time in many years. I was amazed at how soft the recoil felt. I wasn't looking so much at point of impact, as I was shooting at a target about 15 feet away -- just trying the ammo that someone had given me. (It was before this discussion started!!)

I don't think anyone has talked about what happens when you keep the same bullet and reduce the velocity. It will be slower -- will it also hit higher up close? There's less force being dealt with, too...

 

[Limnophile]

Walt,

I don't think anyone has talked about what happens when you keep the same bullet and reduce the velocity. It will be slower -- will it also hit higher up close? There's less force being dealt with, too..

Good point. It's much easier to keep bullet mass constant while varying speed, than it would be to vary bullet mass while trying to keep speed constant -- especially because it appears we have no good way to measure true muzzle speed.

A given bullet launched at a reduced speed should:

- take longer to reach the target, giving gravity longer to act on it; thus, it should impact lower;
- result in longer barrel residence time, giving more time for recoil momentum more to lift the muzzle; thus, it should impact higher; and,
- result in less recoil momentum, reducing muzzle rise; thus, it should impact lower.

Ballistics calculators can give time of flight to target, and bullet drop (which I assume ignores muzzle rise from recoil).

Measured muzzle velocities can be compared and should be somewhat inversely proportional to bullet residence time in the barrel. For example, the 115-gr 9 Luger has a measure muzzle velocity 18% greater than that for its 147-gr counterpart. That relative difference is greater than the relative difference in recoil energy, but I doubt it means the 147-gr bullet spends 18% more time in the barrel.

I haven't shot rounds with different sized bullets in a given range session. I doubt I could tell a difference, because I've failed to feel a difference between my 75 Compact and my .32 Auto 83 in a given session. I may be rather oblivious, as the free recoil energy difference between those two is substantial, although the locked breech design of the 75 absorbs more of that energy than the 83's blowback design does.

I do remember my first time shooting a 1911 being impressed with how much softer the recoil felt than I had anticipated. I assumed it was attributable to the slow speed of the .45 Auto bullet, but the mass of the gun likely has something to do with it, too.

 

[JeffK]

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.

Interesting, real data! So I'm going to claim the only possible explanation for this data relates to how much the barrel tips back (even if not visible in high-speed video) while the bullet is in the barrel - and, all barrels will do this because the recoil action puts a torque on the gun about its center of mass. There's really nothing else that would cause this effect. The final proof would be, a similar set of comparison shots with the gun locked in a vice, so it cannot move even a little bit. The groups should then be essentially identical at close range like 7 yards.

 

[Radny97]

Okay so this just got real interesting. (Forgive me for being slow on this one.) But as I understand it, assuming that the premise of this thread is true (and it very well may be) that if there are two bullets of equal velocity but of different weight shot from the same gun, the heavier bullet will leave the gun at a slightly higher trajectory because the recoil caused by the heavier bullet will tip up the gun more than the lighter bullet before the bullet has exited the barrel . . . THEN will the strength of my grip on the gun also impact this trajectory? In other words if I limp wrist it versus iron fist it, will the limp wrist shot have a statistically higher impact because I allow the gun to tip upward more easily by not aggressively resisting the recoil with my grip?

 

[JohnKSa]

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.

Trajectory differences are based on the distance at which the rounds are zeroed and the muzzle velocity/aerodynamics of the projectiles. Muzzle rise due to recoil is factored into the zero and therefore can't be analyzed by looking at trajectory tables.

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.

That agrees well with the diagrams I constructed and (as you state) also goes a long way towards confirming that there's very little muzzle rise in a 1911 (locked breech pistol) while the bullet is still in the bore.

Very interesting information. Thanks much for the effort that went into posting it.

...does someone have real data showing a bullet rising above the barrel axis after it leaves the barrel?

No. What's happening is that BEFORE the bullet leaves the barrel, the muzzle of a revolver will end up pointing higher than it's pointing at the instant that the trigger is pulled. It's not that the bullet rises above the bore axis, it's that the bore axis angle moves upward during the time the bullet is in a revolver barrel.

. THEN will the strength of my grip on the gun also impact this trajectory? In other words if I limp wrist it versus iron fist it, will the limp wrist shot have a statistically higher impact because I allow the gun to tip upward more easily by not aggressively resisting the recoil with my grip?

Theoretically, if you are shooting a gun that exhibits significant muzzle rise while the bullet is in the bore then your grip has the potential to affect the amount of muzzle rise and therefore the point of impact.

In practice, it might be hard to alter your grip enough to make a significant difference. I can tell you that when shooting air pistols that recoil due to spring-piston movement that altering the grip certainly does make a very big difference. Of course the projectile is moving much slower and the recoil starts much sooner relative to projectile motion in a spring-piston air pistol since the recoil is primarily due to the motion of parts which begin moving "long" before the projectile does.

 

[Limnophile]

Radny,

I am going to guess that a strong grip should help to reduce muzzle rise and could alter POI downward as a result. It's a hypothesis that would be easy to test.

 

[JeffK]

Takes about a millisecond for a bullet to leave a rifle barrel (http://www.frfrogspad.com/intballi.htm), probably less for a handgun. You won't react to anything in under about 200 ms, and barrel rise will commence in the early part of that short time window, so I don't think your grip can have any effect on barrel rise while the bullet is in the barrel. Vices work because of very strong molecular bonds and reactions between different parts of the vice at the speed of sound in the metal (much faster than in air), but your hand isn't a vice. A strong grip will affect the later part of the barrel rise process though, so you can recover more quickly - if it doesn't wreck your accuracy or cause you to flinch.

What's happening is that BEFORE the bullet leaves the barrel, the muzzle of a revolver will end up pointing higher than it's pointing at the instant that the trigger is pulled. It's not that the bullet rises above the bore axis, it's that the bore axis angle moves upward during the time the bullet is in a revolver barrel.

Yes, understood, just making sure no one is talking about bullets rising above the barrel axis, which does not seem possible.

 

[Walt Sherrill]

You won't react to anything in under about 200 ms, and barrel rise will commence in the early part of that short time window, so I don't think your grip can have any effect on barrel rise while the bullet is in the barrel.

Agreed. Reducing recoil after the bullet is gone is important for the reasons you state elsewhere in your response -- in getting back on target.

As soon as the gun is fired, there is some amount of recoil force being applied to the gun in the shooter's hand. And because of bore axis, there will be SOME vertical movement. As you note, none of us can react fast enough to offset the effect of recoil in that first fraction of a second before the bullet leaves. Our physiology just isn't up to it -- our hands aren't a brick wall, either -- there is some give in our grip.

It seems a given that a heavier bullet traveling more slowly will be more affected by recoil-induced barrel rise. One of the earlier responses shows target photos demonstrating that effect with a revolver. Because the barrel and frame of a revolver are single unit, there is no delay in recoil force being passed to the shooter. And bore axis is typically higher.

Semi-autos SEEM to behave differently. The slide and barrel move to the rear as the bullet moves forward, some of the force from the slide/barrel moving to the rear is passed to the frame through a different path - via the recoil spring assembly. After the bullet is gone and the barrel and slide move to the rear and are stopped by their connections to the frame, the more-visible effects of recoil can be seen. The earlier redirected force is passed BELOW the bore-axis on most center-fire semi-autos, and still affects the frame at a point higher than the hand holding the weapon.

The amount of force being redirected can't be much, as the recoil spring is barely compressed. And even then, part of that redirected force is stored. The bullet is gone before the barrel and slide have moved more than a fraction of an inch. But the force redirected (not stored) can't be ignored. A tiny, tiny upward movement of the muzzle before or as the bullet exits will have some effect on point of impact.

The part some of us are struggling with is whether semi-autos, because they delay the immediate full transfer of recoil to the frame, reduce the amount of induced barrel rise. Bore axis is typically less, too. Opinions differ.

I'd like to see the results of a semi-auto fired with the same loads, with the slide locked and left free. If the delay/redirection has an effect on point of impact, it should be visible.

 

[David R]

I will shoot more targets with different weight bullets with a 1911 and see what it does.

Grip has a LOT to do with accuracy especially a S &W.

 

[45_auto]

Grip has a LOT to do with accuracy especially a S &W

Why do you believe that the accuracy of a S&W is more affected by grip than another brand of firearm?

 

[Limnophile]

JeffK,

u won't react to anything in under about 200 ms, and barrel rise will commence in the early part of that short time window, so I don't think your grip can have any effect on barrel rise while the bullet is in the barrel.

But, a strong grip is not a reaction, it is a pre-action. I'm guessing it can make a difference. Again, it's easy to test, but I can't think of an easy way to quantify different grip strengths. However, a qualitative difference -- ie, gripping real hard vs naormal grip vs limp grip -- should be good enough.

Another thought came to me. You can but recoil reduction mechanisms, which are in most cases captured guide rods with a couple of springs that work to absorb more recoil than the stock arrangement. Videos show reduced muzzle rise, the overwhelming majority of which occurs after the bullet has exited the barrel. The reduction is not great visually, but some folks say it makes a difference. And, some report that their pistol's POI noticeably lowers after installing the device. Such an observation seems to be explained by a lessening of muzzle rise prior to bullet exit.

By the way, looking more closely at David R's targets, it appears his bullseye diameter is 1 in, and that his POI for the 158-gr bullets is, on average, 1 in higher than that for the 110-gr bullets. At 7 yd that's a rise of 14 moa, which is huge -- far greater than I would have guessed.

 

[Walt Sherrill]

But, a strong grip is not a reaction, it is a pre-action. I'm guessing it can make a difference.

Perhaps. Maybe JohnKSa should try a firm and less firm grip when he does his comparisons.

I wonder whether that pre-action would have the same effect in revolvers and semi-autos? We still haven't come to an agreement or satisfying conclusion as to whether semi-autos really DO reduce or delay barrel rise. John's range session is a way to look at how bullet weight affects recoil. But we won't know whether semi-autos really do delay or slow muzzle rise before the bullet leaves the barrel. If John could lock his slides we might have evidence for both questions.

With a revolver, the force of recoil begins immediately and is directly transferred from the barrel (bore-axis) to the frame: they are a single unit. (Recoil isn't instantaneous -- it grows as the powder is burned, and that growth ends when the front of the barrel opens as the bullet leaves.) With the revolver, the bore is also on top of a long handle. Pre-action would, in theory, have an immediate effect on the revolver's recoil process.

With a semi-auto, that pre-action is applied to the frame. The bullet fired from the semi-auto, because of the slide and barrels movement, doesn't affect the frame quite as quickly or as directly as bullet movement in the revolver's barrel. There must certainly be SOME recoil force applied to the frame before the bullet leaves the barrel, but the "pre-action" would, it seems to me, have less time to affect barrel rise.

The counter-argument to this idea is that the bullet in the semi-auto barrel has already moved all of the barrel's length and the barrel and slide have moved just 1/10th of an inch. It can't be that MUCH different than a revolver -- recoil MUST be having some effect on SOMETHING! I remain puzzled.​

That said, I've gotten so many other things wrong in this discussion, discussion, maybe this rationale doesn't make sense, either. And if the "delay" of a semi-auto has no effect on muzzle rise, it probably doesn't matter.

 

[David R]

Why do you believe that the accuracy of a S&W is more affected by grip than another brand of firearm?

I should have said consistency. A different grip gives me different groups. More on my smith's than rugers.

Hold firmly, press the trigger gently.
My rim fire Buckmark shoots better with a relaxed grip. It has a muzzle brake. Recoil is minimal so I can just click them off in rapid fire.

David

 

[45_auto]

We still haven't come to an agreement or satisfying conclusion as to whether semi-autos really DO reduce or delay barrel rise.

It should be obvious by the difference between the Point Of Aim (POA) and the barrel axis on a semi vs a revolver.

Front and rear sights on a semi auto are typically almost the same height, which means that the POA is very close to the barrel axis. However, the front sight on a revolver (or fixed barrel like a Contender pistol) of any power will be SIGNIFICANTLY taller than the rear sight. Therefore the barrel axis on a revolver intersects the target MUCH lower than the barrel axis of the semiauto.

What other conclusion can you draw other than semi-autos have reduced or delayed barrel rise during the time that the bullet is in the barrel?

(The difference is that the semi is primarily conserving momentum as linear momentum by using the slide/barrel to compress the recoil spring and hammer spring while the bullet is in the barrel. That momentum is then transferred to the frame and shooter's hand, at which time a significant portion of it is conserved as angular momentum, resulting in barrel rise. Since a revolver has no moving parts with mass to initially conserve the bullet's momentum, the momentum is conserved by the rearward movement of the barrel/frame being turned into angular momentum by the shooters wrist joint while the bullet is in the barrel.)

 

[Bongo Boy]

recoil MUST be having some effect on SOMETHING! I remain puzzled.

Of course it does--it has an effect on everything. The instant there's any relative motion between the bullet and the cartridge case, two semi-independent masses (firearm, bullet) are being accelerated, and both begin moving. What is moving, how quickly and in what direction depends entirely on the components of the 'system' and how those components are coupled. But, the slide doesn't sit around waiting because of its 'inertia'...it has a measurable mass and the force acting on it is measurable, and therefore so is its acceleration.

As soon at the slide begins to compress the recoil spring, the recoil spring acts on the frame, and the frame starts moving. Whether this motion is perceptible or has any practical bearing on shooting depends on all the components of the 'system', which includes the shooter. That includes whether the gun is rotating upward or not and to what degree.

If there was a 5,000 ton freight train sitting on a frictionless track and you walked up and kicked it--it starts moving. It doesn't sit around waiting for a bigger kick or a second one or one it likes--you may have to wait 10,000,000 seconds to measure the distance it's moved, but it's certainly moving.

To suggest a handgun doesn't start moving until the bullet leaves the barrel is to suggest that, when the impulse of the explosion is virtually over with and the force acting on the gun is basically nil, only then does the gun start moving. As though the energy is somehow stored somewhere, then slowly comes into play. That's the way it seems when you kick the freight train--but that's not what's happening. The only reason the gun is moving at all after the bullet leaves the barrel is because it was already moving--now it's just a matter of how quickly the shooter can slow it down.

The perceptible distance the gun has moved is what makes us think it sits around patiently, waits for the bullet to leave the barrel, then picks up speed. It should actually be moving about the fastest it ever moves right at about the time the bullet leaves the muzzle--all the oomph that gets put into the gun has been put it, maximum acceleration has already occurred, and there is no more time for those forces to act to increase velocity.

 

[David R]

What he said!