Advanced Marksmanship The effect of free recoil on POI

[breezernate]

Re: The effect of free recoil on POI

My semi-educated opinion:

Bullets are small relative to the rifle mass, but it takes a lot of force to accelerate a bullet from rest to a muzzle velocity of roughly 3000 fps. This bullet acceleration force is exerted on the rifle/shooter combination before any of the rearward "rocket thrust" effect happens.

When the bullet exits the muzzle and thereby uncorks the high-pressure gasses within the barrel, muzzle blast and most of the recoil occur. This is of course dependant upon caliber, muzzle size, powder charge, muzzle brake, etc. The bullet is gone by this point, but I suppose if the muzzle is moving just at the time the bullet leaves the barrel, these gasses could disturb the bullet as it leaves, causing unpredictable wobbling?

The key I would think would be consistency of launch. One could clamp the rifle in a vice for consistency, or let it free recoil on a string each time. I would think as long as absolute consistency was maintained, so would point of impact.

I agree with Sterling Shooter, holding the rifle firmly seems a better way of building consistency than allowing the rifle to move around on one's shoulder because there are too many variables with that technique. Variables would be: buttstock position, tissue damping and "spring rate", clothing flexibility or "spring rate/fluffiness". Also at play would be coefficient of friction between various types of clothing, which would allow the butt to move laterally unpredictably depending on the clothing worn.

Nate

 

[FranckB]

Re: The effect of free recoil on POI

The gas produced by the burning powder gives a higher pressure inside the case. This pressure is the same everywhere, but there is a moment when the bullet has too much pressure and begins to move to the muzzle. When you are in a small boat, and you want to jump to the ground, each time you end up in the water because, as you jump, the boat goes in the opposite direction. There is a law for that : m1 x v1 = m2 x v2. Your weight x your speed equals the weight of the boat x the speed of the boat (but in the opposite direction, that's why you're wet at the end). With a 5 kg gun, shooting a 0.0116 kg bullet (180 g), at each and every moment, the gun speed (recoil, thus), will be the bullet speed x 0.0116 / 5 (6.96 fps with a muzzle speed of 3000 fps). As soon as the bullet moves to the muzzle, the gun moves to the shoulder (we could consider, too, that the expanding gases moving forward, pushing the bullet, give recoil though the expanging gases moving backwards, pushing the gun, lower the recoil, and adding the Bernoulli's principle, it will end up with a headache...).

After the bullet has cleared the barrel, the expanding gases will push the weapon a bit more backwards, unless something deviates them : a muzzle break.

It is true to say that we feel the recoil after the bullet has cleared the barrel, not because the barrel moves only after the shot (but the expanding gases will actually work after the shot), just because the barrel KEEPS moving backwards. Remember that a shoulder is soft and it takes a little time for the human tissues to be compressed enough, so that we can really feel it.

 

[Topstrap]

Re: The effect of free recoil on POI

I finally got the video posted that kinda demonstrated what I mentioned earlier in this thread about grip tension changing POI. My son is shown shooting his 7-08 XP-100 with sporter weight barrel with a very light grip. The gun does not have a lot of recoil but we've found that type of grip allows us to shoot it much more consistantly than a tight hold. That day he shot a 3 shot group on the 375 yard target that was about 1/2", you can hear the spotter making a comment on it. He's very consistant even though it looks nearly out of control. You can see him adjusting his grip till it feels just right.

http://www.youtube.com/watch?v=eRpZUsog_Jo

That is the way he shoots it and if you watch the entire clip you'll see it does shoot very well including an 8" target at 1000 yards at the very end. If he changes the grip tension or holds a bit more pressure down on the gun or even arm or shoulder pressure it will shoot lower, even more tension it'll shoot even lower. Not sure if this relates to the rifles the same with cheek weld or shoulder pressure but I'm thinking it will but maybe to a slighter degree.

In my way of thinking (non expert) I feel the gun is rising every so slightly as the bullet is traveling down the barrel even though it might be milliseconds. It does not take very much movement to change point of impact at distance. This has been a very interesting thread but still not sure absolute proof has be made yet to satisfy some readers.

At least to us and our thinking it does make a difference for the guns we shoot. I know this thread was probably dead and sorry to bring it back up but wanted to add this video clip as a demonstration of what I was meaning earlier. I think others have made comments about the way they are behind the gun and how it will affect where it hits. If all of that didn't matter then it shouldn't matter how they position behind it and as long as the crosshairs on on the target it should be a hit but it don't work that way. You have to be consistant in all aspects of your shot.

Topstrap

 

[D_TROS]

Re: The effect of free recoil on POI

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Outerspace</div><div class="ubbcode-body">That recent History Channel show on top sniper shots has a number of clips showing the bullet leaving the muzzle, the gun starts to move after the bullet has left on each one. Check it out and judge for yourself. </div></div>

First, sorry to drag up an old thread, but this is what I am into, and I dont think it has been cleared up. Sterling is the guy who has let his trial and error, and mentors, teach him what works. He doesnt have a magic equation to give you an exact number on the deflection of a barrel, but he knows it is there. THe reason for this, is there is no money in doing research to find the equation for deflection when it is so dependant on the external pressures exerted on the barrel/chamber. There is money on making ballistic programs that tell you bullet flight.

I cant believe the patients SS has portrayed in trying to explain this to you outerspace and trippin. The simple scientific fact is that the barrel DOES move as the bullet travels down the barrel. I have done tests myself with strain guages and computer programs a little more accurate than ur naked eye in a slow motion video, which everyone I have watched clearly shows the barrel moving before the bullet leaves the muzzle. There is a force, and there is an equal and opposite force. Not always in the form of recoil.

Here is what happens, the barrel oscilates in a sinusoidal pattern as the bullet travels the barrel. It is on the microscopic level that can really only be measured with computer programs. The barrel essentially "whips" up and down as the bullet leaves the barrel. <span style="text-decoration: underline">The idea for maximum accuracy is to get the bullet to leave the muzzle at the EXACT same time and <span style="font-weight: bold">POSITION</span> each shot</span>. A sinusoidal wave is an up and down motion. The barrel does this and is traveling (whipping/moving/oscilating) the slowest at the peak and trough of the wave. If the bullet exits the muzzle when the barrel is perfectly straight, ie in the middle of the wave when the barrel is traveling/whipping the fastest, the bullet has a higher liklihood of being thrown due to the different position of the muzzle as to the different time it exits. This is why people do load work ups. People alter the amount of powder in a cartridge and the seating depth to "see what load the barrel likes," but are inadvertantly, w/o knowing, ballancing the barrel in its harmonic motion to achieve one of the 2 locations mentioned above when the barrel is traveling the slowest. This way, if the powder load or temp or whatev is not EXACTLY the same (if everything was exact, there would be no challenge in accuracy), there is greater room for error, as the position slightly before the peak is the same as the position slightly after.

Clear as mudd???

Now, how does this relate to the effect of free recoil on POI? Easy, because any, i repeat ANY, change in pressure on the barrel WILL, I repeat WILL, alter the harmonic balance of the barrel. If you have a load work-up that is optimized for your barrel, this change will be minute, but for the purists out there that are searching the one-hole group, this could be the difference between a clean, or dropping a few points. Varying changes can be attributed to the different ways the rifle is handled. This is why barrels are free floated. This is why actions are bedded. To keep consistant force on the barrel/action so your load work-up has a chance to do what it was designed to do. This is also why thicker barrels are "thought" to be more accurate. Because they are. Ha. The thicker barrel will oscillate less than a thinner barrel, meaning the barrel wil whip less, meaning the bullet is more likely to leave the barrel at the same position wach and every time. This is also why it is important to focus on the basics of consistant set up and follow through for each and every shot. Sometimes it wont matter, Like if a primer is hotter than the rest of the batch, or the neck grips the bullet a little tighter, but at the end of the day, everything effects barrel harmonics. And the barrel DOES move at the exact same instant the primer is ignited.

The bullet goes where the barrel is pointed. Easy

Regards,
_DT

 

[Wade]

Re: The effect of free recoil on POI

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Outerspace</div><div class="ubbcode-body">That recent History Channel show on top sniper shots has a number of clips showing the bullet leaving the muzzle, the gun starts to move after the bullet has left on each one. Check it out and judge for yourself. </div></div>

I would recommend that we all base our judgement on our personal shooting experiences rather than a video.

If you don't have them then go out and make them.

 

[Sterling Shooter]

Re: The effect of free recoil on POI

All,

Run a bore brush through a bore, free recoil. The rifle will travel in the direction of the brush. In the next experiment, run a bore brush through a bore, now controlling the rifle as you would such as shooting from something like a sandbag supported position with non-firing hand on handguards. In this second exercise notice the rifle does not move forward with the brush, it can't because the force used to control the rifle is greater than the frictional force of the brush. However, once the brush has cleared the bore notice your opposing force pulls the rifle in the opposite direction. It's kinda like playing tug of rope. Once a tugger lets go the other tugger falls backward. Now, assume the tugger falling backward is the rifle falling back as the bullet having cleared the bore is no longer pulling the barrel yet the shooter is still forcing the rifle, kinda like a human bungee cord.

 

[Graham]

Re: The effect of free recoil on POI

Back-off the rifle and the POI will go up.

It's your hold. Not the bullet.

Free recoil is for heavy BR guns, and maybe for single shot pistols that shoot rifle rounds.

 

[Hellbender]

Re: The effect of free recoil on POI

Recoil actually starts before the bullet even moves in the case.

The primer actually slides rearward in the primer pocket, pushing the case forward and the bolt to the rear (RECOIL) before the bullet even moves.

Outerspace..here's a link that will detail, (probably more than you want) what is going on as the primer is struck.....

http://www.varmintal.com/a243z.htm

It's actually a treatise on polishing chamber walls to differing grades, but there are some very good animations about 1/2 way down on what is actually happening as the primer is struck.

The basic laws of physics are pretty well proven.

 

[Hellbender]

Re: The effect of free recoil on POI

Even before that (primer detonation) the firing pin has mass, and if you dry fire you will see even that can cause significant gun movement....

Don't think you can argue that the FP doesn't move before the bullet leaves the muzzle.

 

[Graham]

Re: The effect of free recoil on POI

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Hellbender</div><div class="ubbcode-body">Even before that (primer detonation) the firing pin has mass, and if you dry fire you will see even that can cause significant gun movement....</div></div>It shouldn't cause any movement.

Nor should the movement of the primer or firing pin translate to moving the POI on the paper.

...and I don't think anyone has even seen what happens inside a chamber at the moment of firing.

 

[Hellbender]

Re: The effect of free recoil on POI

Graham...

It does cause movement, you may not be able to see it, but it does.

Through proper training and practice, we can dampen/control all this movement enough to minimize the effect on target to where it gets lost in other variables....but it is still there.

I was illustrating to Outerspace that many things can happen way before the bullet leaves the barrel if the gun is not properly controlled.

 

[Lowlight]

Re: The effect of free recoil on POI

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Hellbender</div><div class="ubbcode-body">Graham...

It does cause movement, you may not be able to see it, but it does.

Through proper training and practice, we can dampen/control all this movement enough to minimize the effect on target to where it gets lost in other variables....but it is still there.

I was illustrating to Outerspace that many things can happen way before the bullet leaves the barrel if the gun is not properly controlled.
</div></div>

They are buying the line of BS being put out by the guys in that area... that the firing pin movement is causing a loss of accuracy... I said when he presented that argument the first time it would have wings and start to take flight, and less than 30 days later, here it is...

This idea is absolute bs from a lack of understanding so they decided they saw the reticle move during dry fire and figured it was the firing pin moving it. This same movement also claimed a simple firing pin change gave them a 3/4MOA increase in accuracy. Took a rifle shooting over a 1.25 MOA to a 1/2 Minute gun with a $50 solution. Which is why I went out and got two high speed, low drag firing pins to prove this crap wrong before it spreads to Canada, or worse Australia.

Firing pins would have to weight a heck of lot more to move the POI, it would have to be one awful mis-alignment / hole issue to knock things around. Plus we won't mention the lugs are locked in a bit to hold things in place, or the round is in the chamber. Or that the primer gives immediately and flattens out and is not moving the bolt against the lugs because it doesn't weigh enough and craters and flattens.

All this because a guy saw a reticle move and had no idea why, or how to make it "not move"... home grown marksmanship at its best.

 

[Lowlight]

Re: The effect of free recoil on POI

And just to illustrate, If I stand 20ft in front of an 18 Wheeler Tractor Trailer, and sprint as fast as I can head first into the front of it, this is the same as all of what you are saying is true with a firing pin.

I have mass, I am moving against the truck and impacting it, the same laws of physics are present, but i am not moving the truck one bit. If you are not sure, I recommend you try it, you can use a brick wall if you like, I think the results will be very similar as a bolt locked against the lugs. Plus, I am about as big an area hitting the truck as the pin is hitting the bolt and primer.

 

[timelinex]

Re: The effect of free recoil on POI

To substantiate what frank is saying... Anyone that took physics classes should know that there is a big difference between static friction and regular friction. Static friction describes the force it takes to make an object move when it's still versus the force it takes to keep am object moving after it's not still. Static friction is always much greater than the other friction. Before the big event of the explosion , if the rifle is not moving as a whole , a firing pin has so little inertia that it will not move the heavy rifle. Sticking by newtons law theory to explain this is only a valid explanation if u don't fully understand newtons law. Yes, for every action there is a reaction, BUT the reaction does NOT have to be movement the other way. It could be a reaction of heat produced or microscopic crunching or a number of other things. As per his example. If u run into a brick wall, the wall will not move... But that is what many of you are saying will happen. In reality that energy that your directing at the wall WILL cause an equal reaction, but that just means it's pushing as hard on you as you are at it. But as long as the walls friction to it's stabilizing object is greater than the force you exerted it won't move and it will be in place. As simple as newtons laws are , they are easily misconstrued by someone that doesn't fully understand tem.

 

[Graham]

Re: The effect of free recoil on POI

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lowlight</div><div class="ubbcode-body">I have mass, I am moving against the truck and impacting it, the same laws of physics are present, but i am not moving the truck one bit. If you are not sure, I recommend you try it, you can use a brick wall if you like, I think the results will be very similar as a bolt locked against the lugs.</div></div>I have an idea: CKA can document the experiment and we'll use a pole instead of a truck.

 

[Hellbender]

Re: The effect of free recoil on POI

LL- I guess I missed out on the discussion you are describing, as I agree it is stupid to think a lighter FP will make a 3/4 MOA (or any measurable difference in a tactical gun)in group sizes based on FP weight moving the gun. That wasn't my intent of the post.

But I guess I am confused about your statement about dry firing.

Aren't we making small changes in our body position, square shoulders, straight back trigger, etc, etc (as taught in the online training) based on what we are seeing in the crosshairs on target when the trigger breaks??

Isn't this gun movement caused by our body being "un-square" or somehow pushing in reaction to the tiny recoil movement of the firing pin?

And this would translate to a much larger displacement under the actual recoil (pushing harder, longer) of the cartridge.

Or am I totally off base?

 

[Lowlight]

Re: The effect of free recoil on POI

Dry Fire is the Fine adjustment for NPA... the movement is not from the gun, it is from our body.

NPA is not based on the rifle moving but on our reaction to recoil. When you close your eyes, go through a few breathing cycles and open the eyes to see where the reticle is on the target, this has nothing to do with the rifle. You are relaxing the body to see where muscles move the rifle. We talk about Dry Fire to help fine tune as a mental exercise as well as physical one. Remember a lot of shooting is mental.

Trigger control will push on the rifle it has physical contact, how you manipulate the trigger will cause movement in the sights. That whole firing without disturbing the lay of the sights definition. The firing pin moving forward is not causing the problem. <span style="font-style: italic">(unless there is a true alignment issue)</span>

You have a pre-flinch reaction to recoil where your body relaxes at the moment it perceives said recoil, you cannot prevent the muscles from relaxing as it is a built in safety feature to protect ourselves. Shooting a rifle is not a natural act, we are not designed that way, which is why people flinch. The Dry fire movement is a way to trick the body into relaxing the same as a shot so you can see where the fine tune NPA is... it's the same as someone thinking a louder gun kicks more. More of a subliminal message to our body... please relax so I can see what will happen. It doesn't mean the movement of pin is causing it, the sound can cause it. It's just what the body needs to know in order to perform as directed.

Why do you close your eyes and breath to check NPA ? To mentally relax your body, the idea is to not focus on the rifle, but to let the body rest in position so the rifle will settle in along with the muscles. This relaxation moves the rifle / sights either off the target or they stay on based on your position. If you find the sights have drifted you then move ever so slightly and repeat. Once the gross adjustment is made, you then Dry fire to test the position, as well as test and practice your trigger control which can also move things... Poor trigger control is accuracy killer number 1, this can be visible also. Snapping the trigger, slapping it, tapping it, all will cause movement. So people feel because they can take their handloads, shoot a 1/4" group here and there they have proper trigger control. This is not always the case, the same flawed thinking can also fool them into believing something else is at work. <span style="font-style: italic">(firing pin movement)</span> Plenty of people with light triggers can "tap" the trigger and find a sub 1/2" group downrange, completely dismissing Follow Through, but that same lack of Follow Through can move the reticle because the trigger is moving.

During the gunsmithing class when I was threading the barrel, I stopped the machine on several passes at .00430" this was my hand / eye coordination at work. I heard the tool stop cutting, saw it reach the relief gap and landed on this spot time after time. Robert even commented to me how consistent this was, and how accurate our brain can be. This accuracy can help or hinder by providing consistent results with less than perfect technique. I wasn't watching the read out, was watching and listening to the tool... good or bad, habits are consistency which show themselves in a variety of ways.

 

[Greg Langelius *]

Re: The effect of free recoil on POI

How refreshing to see the snake oil being dispelled.

Sure, lots of things are happening as the lock time transpires.

But to blame them for gross POI displacement is pretty similar to the famous Flip Wilson/Josephine Defense ("De Debbil made me do it").

Those mechanical things happen precisely the same for every shot, and the combined consequence of their effects on dispersion are so small they are lost in the 'background noise' of environmental variables.

The rifle, shooter, and environment constitute a single system. The rifle and ammo are consistent enough, even in their unrefined form, to transfer the major bulk of inaccuracy origins onto the shooter.

If the shooter recoils the same; then recoil exerts a minimal effect on dispersion. Whether one is a hard holder, a relaxed rider, or an impact obstacle for a free recoiling firearm; so long as they do it the same each time, the outcome is consistent.

Me, I hold 'moderate', relax, and ride out the recoil cycle. I don't have any illusions about being as consistent as a mechanical rest, but I try my best to avoid concentrating and influencing the body's natural cycle of displacement and return to its preceding state of relaxed equilibrium.

For me, the key mental components of my shot are to get the starting position back to a proper initial point, then concentrate on sight picture and trigger squeeze.

Trying to add more concerns during this key phase simply overloads the processor and impairs its ability to do the crucial eye/finger maneuver.

Greg

 

[CoryT]

Re: The effect of free recoil on POI

I find it amazing that this thread has gone on for 7 pages. As Mark Twain once said, "It's not what you know that causes the trouble, it's what you know that just ain't so."

Outerspace, if nothing moves prior the the bullet exiting the barrel, then why do we have locked breach semi-autos instead of everything being straight blowback? If you are trying to see .01 inches of movement in a youtube video you are delusional. The barrel is moving as soon as the bullet starts to move, Newton was not wrong. The amount of that movement is very small, true, but it is an angular issue that increases with distance. If 1 MOA = 1.047" at 100 yards, at 1 yard it's .01047". That's not visible no matter how fast the frame rate is, you don't have the resolution.

The idea that the gas jet is producing the recoil is pretty funny. The fact we converted x grains of powder into x grains of gas does not equate to much recoil, since much of the energy is heat. Do blank guns have much recoil? It's barely discernable, but the gas jet is still there.

The FP thing is just as funny. With modern firearms, lock time is so short as to be non-issue. Whatever motion is there during the 30ms or less the firing pin takes to fall is due a lot more to the shooters reaction to the sear release than the fiing pin mass. Now, with a flintlock, the whole thing changes.

 

[Massoud]

Re: The effect of free recoil on POI

I want to add a couple things to this to correct something.

A locked breach is locked to contain the relatively massive force of ignition, which would immediately move the bolt if it was in a blowback type of setup, that is a good point CoryT. Look at a short recoil operated weapon (M2 is one) to get an idea.

However, Cory is wrong about the recoil formation not being due to a jet of gas. This has been understood and exhaustively studied by DOD, Brits, Germans, et al for 100 odd years now. The gas upon exit acts as a rocket nozzle. If you would like to read about 2k pages on muzzle brakes and recoil, go to dtic and start poking around.

Think of it this way, if there was no effect from the "exhaust gas" at the muzzle, what would adding a muzzle brake do? Nothing. Yet we know that muzzle brakes can reduce recoil up to 80 percent in the more efficient implementations.

I personally have only fired a blank through a bolt gun a couple times and don't remember if there was any recoil, however in a semi-auto, bear in mind much more of the gas is directed back to actually operating the weapon and the bore is really choked down at the muzzle. Perhaps someone here could run a blank round through a lightweight bolt gun. Since there is no projectile, any recoil would come from the the movement of the relatively light powder charge and the gas exiting the muzzle. I would suspect we could neglect the mass of the powder charge as a cause of felt recoil in this instance.
Justin

 

[CoryT]

Re: The effect of free recoil on POI

Certinaly the gas jet is part of the recoil force, it's just not what creates recoil. Captive piston rounds still have recoil, there is no gas jet at all.

The great majority of recoil force is generated by the work of the expanding gas moving the weight of the projectile. This is why a lighter bullet load has less felt recoil, despite having a larger powder charge for increased velocity.

 

[Massoud]

Re: The effect of free recoil on POI

Cory, there's no question that accelerating a bullet causes some recoil. I'm not sure what you mean when you say the gas jet is part of the recoil force but does not create recoil. The gas jet creates recoil, or maybe more properly "creates rearward momentum", there is no question about this. In fact I'm saying it creates more recoil than accelerating the bullet.

Here's a few examples:

A recoilless rifle uses a projectile that is many orders of magnitude heavier than a bullet, however the launcher itself is, practically speaking, the same weight as our target rifles. How can this be? If what you say is true, launching a recoiless rifle round would create such a recoil force that no one could hold the launcher. However it in fact has no recoil whatsoever because the gas jet is pointed straight rearward and is vented through a de Laval nozzle.

A newish idea for recoil reduction is called Rarefraction Wave Gun Propulsion (RAVEN). This system vents combustion gasses in a gun before the actual projectile exit of the bore. These gases are directed rearwards. A rarefraction wave is formed which isolates the pressure drop from the projectile. This yields a reduction in recoil of upwards of 60% while not decreasing muzzle velocity of the projectile. The authors of that study concluded that a zero recoil system could be achieved with the RAVEN and a good muzzle brake. Here is the info: Rarefaction Wave Gun Propulsion (RAVEN), 18 MAY 2002, Rensselaer Polytechnic Institute, Troy, NY

CoryT, I'm open to hearing any counter evidence you have that would suggest that recoil is mostly a function of bullet acceleration but so far you have offered no support to that opinion.


How about an experiment, take a good magnum caliber in a light hunting rifle, like a 300 RUM, load some 110gr vmax and some 220 gr SMKs. Pick a good efficient muzzle brake, then ascertain the difference in recoil between the two bullet weights, and the difference in recoil between shooting with and without a brake. I'm just about 100% sure you will see a greater recoil reduction with the brake vs going to a lighter bullet.

Justin

 

[CoryT]

Re: The effect of free recoil on POI

What I'm saying is that the gas jet itself does not create the recoil force. My 'proof' if you will, is a captive piston round. The most available of these is a Simunitions or UTM round. There is no gas vented from the muzzle, only a projectile. There is enough recoil generated to run a semo auto action.

The Venturi nozzle accelerates the gas in the recoilless system to counteract the projectile launch. I'm not sure what that has to do with a locked breach system that has no high pressure nozzle. In fact, the forces are not really fully balanced and a 'recoilless' system normally does have some recoil.

http://en.wikipedia.org/wiki/Recoil

Here you can see the formula for calculating recoil force. The weight of the powder charge is part of that calculation, as it is part of the moved mass. If you remove the weight of the powder charge, you'll note that there is little reduction in the answer, since the powder mass is only a fraction of the moved mass.

That the velocity of the ejected gasses can be captured against the baffels of a muzzle break and used to counteract some of the recoil force does not indicate that the gasses are the causal element in recoil. I refer again to a blank round. Run a full powder charge blank and see how much recoil you feel compared to launching the mass of the bullet. A blank round recoil is limited the the acceleration of the powder mass. This is why a restrictor port of some type must be installed in a semi auto to get it to function, even in a blowback system. A recoil type system will normally require the removal of the lock, since absent the projectile mass there is nowhere near enough recoil energy to operate the gun.

 

[Massoud]

Re: The effect of free recoil on POI

I've already agreed that accelerating a mass causes a recoil force. This was shown far above by a poster actually detailing out the math. This is in no way "proof" that the gas jet has no contribution to recoil. You're looking at those equations too simplistically. The equation is showing you the recoil generated by accelerating a certain mass to a certain velocity by a device of a certain mass. The equation is not telling you the total recoil force generated by a firearm during firing. The system in the equation could be the Large Hadron Collider, a guy throwing a spear, etc.

You keep mentioning a blank round which is an error. What a blank lacks is pressure. A blank in an open gun barrel is basically a bit of gun powder in an infinitely large pressure vessel. You could just as easily pour that pile of powder from a blank onto the table and light it and see if there's any recoil created. There won't be of course. A real round is completely different. Granted, the crimping of the tip of a blank would allow some pressure to build, but not 60ksi which is right around a modern cartridge pressure. If you uncorked 60ksi, like at the muzzle upon bullet exit (yes I know it's not 60ksi at that point), I guarantee you would see recoil. In evidence of this, think of those little race cars that guys build in high school shop. They use a CO2 cartridge for power. I pin pierces the cartridges, unleashing the pressure inside. This makes the car take off like a what...a rocket. Yeah it's the same exact principle. No de Laval nozzle needed on those little cars by the way. Now in what way is the muzzle of your rifle different from that little car with the hole poked in the CO2?

A restrictor is required for blanks to raise the gas port pressure to a sufficient level to cycle the action. This has nothing to do with recoil. On straight blowback, as you correctly mentioned, the recoil force of just the powder mass is insufficient. You also proved my point when you said that to make it function, you add a restrictor (which ups the pressure causing more force against the bolt). Note here how more force is created in the absence of any heavier projectile, meaning essentially that "recoil" force is created by manipulating gas.

This sentence, "That the velocity of the ejected gasses can be captured against the baffels of a muzzle break and used to counteract some of the recoil force does not indicate that the gasses are the causal element in recoil" is a contradiction.

Here you admit that manipulating (redirecting basically) exit gases can in fact reduce recoil yet you claim that non manipulated gases do not contribute to recoil. Those two concepts are opposing and are mutually exclusive. Either gas causes recoil and can be redirected/manipulated to relieve recoil or gas does not cause recoil and no amount of manipulation will affect recoil.

I realize that you are not going to come around. Trust me this is an argument you cannot win. Not because I'm a super smart particle physicist, but because you are arguing against 100 plus years of research done by DOD (I'm including all the arsenals, labs, etc), and physics of course. You cited wikipedia when I gave you an actual academic paper you could read.

Look, every thought about guns that you have ever had (or me or anyone else on this board) has already been thought about, written about, and tested by one or more military entities. Muzzle brakes, barrel linings, caseless ammo, everything. All that stuff is out there, well some is still classified, at dtic.

We're now far off the original topic of free recoil affecting POI. If you'd like to continue this discussion on recoil, which has been enjoyable, I would suggest making a new thread and we can bring in even more knowledge and really hash this out to clear up any misconceptions. I would be happy to actually quote and cite sources as I'm sure you would and others as well.

Justin

 

[CoryT]

Re: The effect of free recoil on POI

I never said it had no contribution to recoil. What I said was it is not the causal factor, that without the gas jet, there would be no recoil, which is what you are implying.

Take any recoil operated pistol. Make a blank round using a normal powder charge. Plug the end of the barrel, then drill the plug with say a 1/16" hole. You'll get near full pressue, relieved via the small port just like your CO2 cartridge powered car. The gun will not cycle. You can install any kind of nozzle you want, it's not going to run. Why? The recoil force generated by the ejected gasses is far too small to move the working parts. It does not weigh enough. A gas operated gun with the same restriction port will work just fine, since the pressure in the barrel will be enough to drive the system just like a live round. Felt recoil will however be nearly non-existant. The 50k pressure is there, release just like a live round, but only the mass of the powder charge has moved forward.

The CO2 cartridge has VOLUME, much more gas than a small arms powder charge. Once the bottle is uncorked (the barrel), the pressure drops to near zero in milliseconds. The CO2 cartridge continues to vent, the pressure drops over more than a second, moving much more mass as part of the gas jet. A typical cartridge has 16 GRAMS of gas, not 40 or 90 GRAINS. That is the differance between your car and a rifle, plus the weight of course.

If you do the math for 90 grains of gas at 60k psi for even 10ms against a 10 pound rifle, you won't move the rifle very far.

Note, I did not say non-existant, just minimal.

 

[cali_tz]

Re: The effect of free recoil on POI

The varying opinions at least make one think hard about the problem... great thread.

 

[Indypendent]

Re: The effect of free recoil on POI

Hahaha, I would charge money for people to gain access to this thread. I love it!!! It's these types of discussions that makes shooters in to physicists and then in to ballisticians and then back in to shooters again...hopefully.

I'm hooked....keep going.

 

[Arbiter]

Re: The effect of free recoil on POI

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: CoryT</div><div class="ubbcode-body">I never said it had no contribution to recoil. What I said was it is not the causal factor, that without the gas jet, there would be no recoil, which is what you are implying.

Take any recoil operated pistol. Make a blank round using a normal powder charge. Plug the end of the barrel, then drill the plug with say a 1/16" hole. You'll get near full pressue, relieved via the small port just like your CO2 cartridge powered car. The gun will not cycle. You can install any kind of nozzle you want, it's not going to run. Why? The recoil force generated by the ejected gasses is far too small to move the working parts. It does not weigh enough. A gas operated gun with the same restriction port will work just fine, since the pressure in the barrel will be enough to drive the system just like a live round. Felt recoil will however be nearly non-existant. The 50k pressure is there, release just like a live round, but only the mass of the powder charge has moved forward.

The CO2 cartridge has VOLUME, much more gas than a small arms powder charge. Once the bottle is uncorked (the barrel), the pressure drops to near zero in milliseconds. The CO2 cartridge continues to vent, the pressure drops over more than a second, moving much more mass as part of the gas jet. A typical cartridge has 16 GRAMS of gas, not 40 or 90 GRAINS. That is the differance between your car and a rifle, plus the weight of course.

If you do the math for 90 grains of gas at 60k psi for even 10ms against a 10 pound rifle, you won't move the rifle very far.

Note, I did not say non-existant, just minimal.</div></div>

I think the argument between you and Justin has been based on the mistaken premise as to whether the gas jet exerts any recoil force at all, whilst both parties freely admit and realize that there obviously IS some degree of recoil force imparted, whether it's significant or not. I'm not an engineer, but I'd think it would be very straightforward to calculate the kinetic energy imparted by a given mass of gas traveling at a certain speed, and then compare it to the energy of the bullet at the muzzle, no?

The main reason we have this thread in the first place appears to be because someone failed to realize that just because they couldn't visually see movement of a muzzle before the bullet exited, that there wasn't any movement present. Our eyes, even aided by high-speed photography, are still capable of deceiving us. And in the science of long range shooting, even that 0.01" of movement an earlier posted mentioned is more than enough to have a significant influence upon impacts on a target positioned 1000 yards downrange.

 

[tpr564]

Re: The effect of free recoil on POI


Lot of nerd rage in this thread.

 

[dwt]

Re: The effect of free recoil on POI

I finally got around to reading this whole thread,you guys need to get away from the computer and out to the range and shoot more !!!

 

[RackSqueezeBang]

Re: The effect of free recoil on POI

I'm going the opposite direction.

Through a bit of luck, I have seen with my own eyes high speed film of a bullet leaving the muzzle, and the bullet is long gone before the muzzle rises or a bolt/slide racks/moves in a semi-auto rifle, handgun, no question about it. It's gone before anything moves.

I have seen this 3 different times, with a bit of youtubing maybe people can find more examples or prove me wrong, I don't have an agenda either way, just the times I saw it the bullet was definitely clear before anything moved on the gun.

Shifts in POI when changing positions may be due more to parallax error, ie your eye is in a slightly different spot when you are standing vs. prone, etc.

I don't claim to know everything but I do think the above is worth considering and investigating. After I saw film I never worried about recoil again.

Just for curiosity, I’d like to see this kind of video on a shooter who has poor fundamentals. A good shooter with good fundamentals would be expected to produce these results. So the question is will these results stand with poor fundamentals, or will there be movement in the barrel.

I also wonder, assuming there is in fact movement before the bullet exits the barrel, is the movement of the barrel even enough to be perceptible if for instance the POI has shifted by even a 1/4” at 100yds.

 

[KnowNothing256]

Just for curiosity, I’d like to see this kind of video on a shooter who has poor fundamentals. A good shooter with good fundamentals would be expected to produce these results. So the question is will these results stand with poor fundamentals, or will there be movement in the barrel.

I also wonder, assuming there is in fact movement before the bullet exits the barrel, is the movement of the barrel even enough to be perceptible if for instance the POI has shifted by even a 1/4” at 100yds.

It’s well known that the gun moves before the bullet is gone; this is just physics. Gun applies force to bullet to accelerate it, bullet applies that same force in the opposite direction (really it’s the gases from the burning powder that do the pushing in both directions, but that’s minutiae).

It takes very, very little muzzle movement to cause a detectable POI shift. If someone really wanted to see this phenomenon, they could put a dial indicator on the end of the barrel and shoot a high-speed video. I guarantee that needle moves.

 

[RackSqueezeBang]

It’s well known that the gun moves before the bullet is gone; this is just physics. Gun applies force to bullet to accelerate it, bullet applies that same force in the opposite direction (really it’s the gases from the burning powder that do the pushing in both directions, but that’s minutiae).

It takes very, very little muzzle movement to cause a detectable POI shift. If someone really wanted to see this phenomenon, they could put a dial indicator on the end of the barrel and shoot a high-speed video. I guarantee that needle moves.

That’s what I always understood as well. Good idea on using a dial indicator.

 

[Mr. Z]

I’d bet their opinions have changed in the 12 years since this thread has had a reply before today…

 

[Baron23]

The barrel essentially "whips" up and down as the bullet leaves the barrel.

I have asked many times and have yet to hear a cogent explanation....why "up and down". Why is the vector sum of movement in the barrel not side to side. Or at a some degree in between. Its a round tube.

This seems to come up often in discussions about "positive compensation" and I have never understood the basis of it.

 

[KnowNothing256]

I have asked many times and have yet to hear a cogent explanation....why "up and down". Why is the vector sum of movement in the barrel not side to side. Or at a some degree in between. Its a round tube.

This seems to come up often in discussions about "positive compensation" and I have never understood the basis of it.

I'm not convinced it's only up and down, if we're talking about whip. I see windage movement when I do an OCW most of the time, which makes total sense to me.

But the POI shift from free recoil should just be vertical, as long as the rifle doesn't recoil with rotation around the vertical axis (the line of gravity) when free-recoiled. Put another way, if the rifle is level and so is the support, it should only rock up, not turn left/right, under free recoil.

 

[D_TROS]

I have asked many times and have yet to hear a cogent explanation....why "up and down". Why is the vector sum of movement in the barrel not side to side. Or at a some degree in between. Its a round tube.

This seems to come up often in discussions about "positive compensation" and I have never understood the basis of it.

holy necro post. haha good stuff.


thats a great question and ill have to check my text books from school. i believe up/down is purely "anecdotal" as we can visualize it with a up/dwn graph when in reality its vibrating all over the place. but vibrations are sinusiodal and do whip back and forth till they stop vibrating.

i never put strain gauges in diff locations and that would be cool to test out. I no longer have access to that kind of equipment or the time to do so.

that would be why when you shoot groups they can be centered up left down right etc etc as the barrel is vibrating in diff directions. you do load work up to minimize the group where ever it is. then the bullet leaves the vibrating barrel at close as poss to the same location ea shot...when the flex is changing directions its moving the slowest which allos the greatest error in variables.


ish...lol


GL
DT

 

[Baron23]

I'm not convinced it's only up and down, if we're talking about whip.

yes, I'm absolutely not convinced its only in the vertical and...well, whip is one word for it...vector sum of all vibrations resulting in oscillation...maybe...right?

And if I gave the impression that I thought this was related free recoil that's my bad. But people always seem to discuss the effect of barrel oscillation from firing as only expressing itself in the vertical.

Or at least that's my limited understanding of discussions on positive compensation.

Cheers

 

[Baron23]

holy necro post.

LOL...but I'm not the one that dug up the grave...haha...thread was refreshed before me.

in reality its vibrating all over the place. but vibrations are sinusiodal

I'm not a mechanical engineer...but, my limited understanding is that these vibrations will sum to a sinusoidal wave form that can be in any direction...vertical, horizontal, or more likely somewhere in between depending on barrel and load characteristics. We seem to be in violent agreement.

Thanks for the reply.

Cheers

 

[Bks22345]

I'm not convinced it's only up and down, if we're talking about whip. I see windage movement when I do an OCW most of the time, which makes total sense to me.

But the POI shift from free recoil should just be vertical, as long as the rifle doesn't recoil with rotation around the vertical axis (the line of gravity) when free-recoiled. Put another way, if the rifle is level and so is the support, it should only rock up, not turn left/right, under free recoil.

I disagree, you have torque due to the rifle twist. I have a 284 with an 8 twist barrel (f-open) and no break. If I set it up on front and rear rests, remove my body and just pinch the trigger it will recoil straight back, but the right edge of the stock will lift about 3/8”. This causes vertical and horizontal.

This is an extreme example but I expect there are minute amounts of rotational movement even if you are hard holding.

 

[Rio Precision Gunworks]

The person who was quoted from 2011 likely saw video of a barrel that was in a rest that didn’t allow the rifle to pivot/lever vertically.

You’ll see the barrel move vertically before bullet exist if the rifle can pivot. If it’s only allowed to move rearward, you’ll see the barrel moving to the rear before bullet exist but you’ll be hard pressed to visually see the “whip” or “harmonics” everyone talks about.


As far as free recoil, the heavier the rifle, smaller the cartridge and longer the support (like a barricade bag), the less vertical dispersion you will see.

Take a lightweight .308 and free recoil. Then take a 25lbs 6mm in a competition chassis and free recoil. The 6mm will have almost no vertical dispersion compared to shooting prone or fully supported. The .308 will have noticeably more vertical.


As far as the harmonic/whip part being discussed , yes, it’s ridiculous everyone only focuses on the vertical when PC and tuner discussion pop up. For many reasons.