Weird things with .22LR match ammo

_Shorty said:
Finding the BC of every bullet will tell you how much of any POI changes you see might be due to bullet imperfections. Finding the BC of every bullet literally tells you whether the bullet was in good shape, average shape, or beat up. And finding the BC for a whole bunch of them tells you how good or bad any manufacturer is at keeping bullets in good shape. I don't know why you say it is invariably because of bullet imperfections. There's more than one reason for it happening, and that statement of yours literally means that is the only reason, which is not correct. I don't think your words were chosen carefully there. But finding the BC of every bullet will tell you how much of a difference you should've seen on target because of it, and the target itself will tell you whether or not there was that much difference. And when the two don't align, that tells you there are also other variables at play, which I've already tried to illustrate.
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You say you don't know why I said that bullet imperfections are key to understanding why MV and POI mismatch may occur. I'll attempt to explain again for readers in general.

Among well formed .22LR match bullets, the key imperfection remains center of gravity variation between bullets and lots of bullets. This has little if anything to do with variation in weight between bullets.

I didn't "invent" the idea of bullet imperfection in the form of center of gravity issues. Despite how new or unfamiliar it may appear to any readers here, rest assured that it's an established idea. For example, it's discussed by Harold Vaughn in his highly regarded book Rifle Accuracy Facts, published, I believe, in 1997. As a professional ballistician and supervisor of the Aeroballistics Division of the Sandia National Laboratories in Albuquerque from 1959 to 1986, Vaughn certainly had the qualifications to back up what he wrote about.

Vaughn's work corroborates and informs the study of .22LR match ammo ballistics done by Larry "Landy" Landercasper, a well respected amateur ballistician who posts on Rimfire Accuracy and other forums under the name HuskerP7M8. As Landy puts it "there is no doubt whatsoever imbalanced bullets are a major source of dispersion as per Harold Vaughn's "Rifle Accuracy Facts". Dispersion is what is seen as bullets spread out in different directions from the POA and form groups that are of varying size. In other words, the greater the dispersion, the larger the group.

Landy, who has his own testing tunnel with a sophisticated chronographing system, reminds us that the two main causes of dispersion with .22LR are MV variation and bullet Cg variation. The two combined help explain why some ammos with the same MV variation produce different dispersion patterns.

The thing to remember is that unlike jacketed centerfire bullets, .22LR lead bullets are very difficult to manufacture without center of gravity issues. This means that bullet center of gravity will vary between lots, indeed can vary between bullets within a lot. Cg variation explains why some lots of the same kind of ammo do better than other lots of the same ammo, especially as distance increases. And since each rifle can contribute to Cg variation by means of its unique obturation of the bullet as it goes from chamber/leade to muzzle, different rifles shoot the same ammos with different rates of dispersion.

For the average shooter it's impossible measure a .22LR bullet center of gravity. We can only see the effects downrange. It's also impossible to know the MV until the round is shot. Excluding the influence of wind, MV and Cg variation combine together to explain dispersion rates. When a bullet has an unexpected center of gravity variation, the result will be an unexpected POI.
 
"The reasons why MV and POI don't always match are invariably due to imperfections in the bullets themselves." That's what you said. What you said means there's no other cause. Bullet imperfections are not the only cause. There are multiple causes. So, like I said, you probably just didn't choose your words carefully. I'm pretty sure you meant something more like "are often caused by." But if you actually do think abnormal POI is caused by nothing other than bullet imperfections, well, sorry, that is wrong. It is a cause. It is not the only cause.
 
_Shorty said:
"The reasons why MV and POI don't always match are invariably due to imperfections in the bullets themselves." That's what you said. What you said means there's no other cause. Bullet imperfections are not the only cause. There are multiple causes. So, like I said, you probably just didn't choose your words carefully. I'm pretty sure you meant something more like "are often caused by." But if you actually do think abnormal POI is caused by nothing other than bullet imperfections, well, sorry, that is wrong. It is a cause. It is not the only cause.
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I said what I meant to say. Bullet imperfections result in differences between bullets. Bullet differences or bullet imperfections cause MV/POI mismatch. When all is equal and excluding wind, MV and POI will have a consistent and predictable relationship. When that doesn't occur, it's because of bullet differences -- or, in other words, bullet imperfections.

______________________

To simplify the problem, readers are invited to consider the following. To keep things straightforward, there is no wind or air movement involved.

A .22LR match round has a bullet that is perfectly formed and symmetrical and has a perfect center of gravity is shot with an MV of, say, 1070 fps. It is shot from as good a rifle as is made with a barrel that has as good a chamber/leade and bore that it doesn't alter the bullet's center of gravity. All bullets shot from this barrel are obturated equally.

A second round also has a bullet that's perfectly formed and symmetrical and has a perfect center of gravity. This second bullet is shot is shot from the same barrel at exactly the same POA. It has precisely the same MV as the first, 1070 fps. Again, no wind, no air movement.

All else is the same, too, including environmental things such as temperature, air pressure, altitude. Gravity is immutable. The only thing different might be if the shooter had a sip from his coffee cup between the first and second shots, but of course that won't affect the flight of the bullets.

These two bullets are identical in every way. They are perfectly formed, perfectly symmetrical, perfectly balanced. They are both shot in exactly the same environmental conditions. They both leave the muzzle at exactly the same MV. They both never increase their respective velocities and because the bullets are identical they will both decelerate at exactly the same rate until the end of their flight.

With all things being equal, is there no reason to expect that they will not strike with the same POI. It's when there are imperfections in the bullets that problems arise. Bullet imperfections mean that bullets aren't always identical. Under identical no-wind conditions with the same MV, it's only when the bullets are different that they will have different POIs.

Shorty claims that there are "multiple causes" for MV/POI mismatch. When wind or other conditions are not involved, what other forces can cause identical projectiles shot with identical MVs (from the same barrel) to have different POIs? I invite Shorty (or any reader) to identify one or more of the other "multiple causes" he claims will affect POI.
 
I already told you another cause before, but you can't seem to understand it. Primers and powders do not burn at a uniform rate. Two shots with the same muzzle velocity do not necessarily have the same acceleration curve inside the barrel. But for whatever reason you think this is impossible. You think if they have the same MV then they by definition must have the same acceleration in the barrel. Why you can't seem to wrap your head around this idea, I do not know. It is very simple and straight forward, but somehow you cannot grasp or accept it. Two shots with the same MV can take different amounts of time for the bullet to exit the muzzle, and this causes different launch angles for each. They will have a different POI that is not due to bullet imperfections.

I know people with insanely expensive laboratory balance scales they use during their reloading process. And they have loaded rounds to their desired target powder weight to within a single kernel of powder, for an entire reloading batch. Hundreds of rounds that all contain the same amount of powder right down to a single kernel. And a single kernel of powder is well outside that scale's error range. So it is very fair to say that they have the same amount of powder in every single case. And they take extreme care to load all rounds to the same bullet seating depth, too. They do their best to eliminate all the variables they can in their rounds because they are used for long range competition, and they need them to all perform as closely to the same as they possibly can in order to get their muzzle velocity SD and ES as low as it possibly can be. Even loaded to within one kernel of powder of the same weight, they still have non-zero SD and ES results. How can that possibly be? All their powder weighs as close as humanly possible to the same weight. Why on earth would they have differing muzzle velocities? Because the primers and powder do not have burning rates with zero SD and ES. Every example of primer and powder burn at slightly different rates. This is precisely why the pressure traces I showed you before have little wiggles in them rather than smooth lines, because the powder burn is speeding up and slowing down, speeding up and slowing down, the entire time it is burning. If the powder were burning at exactly the same rate the entire time there would not be any tiny little wiggles in that pressure trace graph. But there are little wiggles. And the little wiggles are from the varying burn rate of the powder. And that varying burn rate gives a varying acceleration rate. And that varying acceleration rate gives a different barrel time, even when MV is the same. And varying barrel time results in varying launch angles. And varying launch angles are another cause of varying POI. So, no, bullet imperfections are not invariably the cause of varying POI when the MV is the same, because varying barrel time is another cause.
 
_Shorty said:
I already told you another cause before, but you can't seem to understand it. Primers and powders do not burn at a uniform rate. Two shots with the same muzzle velocity do not necessarily have the same acceleration curve inside the barrel. But for whatever reason you think this is impossible.
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Shorty, it's been explained in previous posts why you are wrong. As in previous posts you continue to claim it's because bullets with the same MV can have different "acceleration curves" and that those different curves mean bullets behave differently.

More specifically, you insist that, even without wind influence and all else the same, different "acceleration curves" will explain why two perfectly formed and identical bullets with the same MV, shot from the same good barrel at same POA can behave differently from one another as they go to the target.

This view is specious.

The fact is that two .22LR bullets with the same MV must go through the same barrel in the same way. They both start at 0 fps (0 mph) in the chamber/leade and go to, say, 1070 fps (about 729.5 mph) when they exit the muzzle. Whether the bore is 16" or 26" in length, two bullets must accelerate identically in order to have the exact same MV when they leave the muzzle.

This is because unlike cars, which can alter their power along the way because they bring their engines along for the ride, bullets have a one-time-only source of power -- the ignition and burn of the powder in a brief moment. Once the firing pin strikes, no matter the make-up of the combustion, the source of energy is released. Once the energy is released, any bullets going through the same bore to the same MV must have the same rate of acceleration. There are no other ways to get to there. They can't independently or figuratively slow down, take a coffee break, or step on the gas to make up for any lost time. They take what they got and go to the muzzle. There are no different "acceleration curves".

Unfortunately for Shorty, his view is untenable and without supporting evidence. Of course, if any reader has an explanation supported by reliable source to validate Shorty's views it would be most welcome.

__________________

Incidentally, the view that bullets have a variety of unpredictable ways to get from 0 fps to the same muzzle velocity due to differences in "acceleration curves" would make reliably repetitive tuner use impossible. When tuners work effectively its because "barrel harmonics" are predictable, which is to say the barrel will "vibrate" in the same way for rounds with the same MV.

Different and unpredictable acceleration curves would mean different and unpredictable -- random -- barrel harmonics. This would make tuning with a barrel tuner impossible because barrel harmonics would always be potentially different even for rounds with the same MV.
 
hobit said:
The .22 guru has spoken, everyone else just read and have no opinions ... what a self important windbag!
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Lol this is what he does. He posts his opinions as if they were facts, then totally disregards other people's opinions while reiterating his own. Just the kind of guy that loves the sound of his own voice. It's kind of funny.

His thread about a single flyer and a flash he caught on camera, and there being some sort of correlation is a good read too, lol.
 
_Shorty said:
grauhanen, powder does not all burn at the same rate. I don't know why you cannot understand that. It is a simple matter.
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Not only does powder not burn at the same rate... but if you have two different lengths barrels as said above... the bullet physically ineracts and thus accelerates at different rates due to the friction and interaction with a longer or shorter bore.

A few people have mentioned CG with respect to the projectile, but that is only one part. Center of pressure is equally important, not measurable by the every day person, and is directly tied with CG, and thus how the projectile flies through the air.

Barrel harmonics aren't only tied to MV either, LOL. Harmonics are affected by the initiation and containment of the powder being burned, and thus sending vibrations down the barrel - which equally affect the muzzle pointing variability. Shot release and muzzle pointing variability are hugely important in minimizing dispersion, along with consistent projectiles, which can otherwise affect both the static and dynamic stability of the projectile through its time of flight.

Assuming two projectiles with the same velocity at shot exit exhibit the same acceleration in the same barrel is hilariously dubious - every manufacturer formulates their powder(s) to achieve a desired pressure and velocity at shot exit. They can use a slow burning powder, or a faster (relative to each other), both charges could result in the same velocity at exit, but have entirely different pressure curves, burn rates, and time to complete burn.

Sounds like this expert doesn't actually understand interior ballistics all that much.
 
Scotty454 said:
Lol this is what he does. He posts his opinions as if they were facts, then totally disregards other people's opinions while reiterating his own. Just the kind of guy that loves the sound of his own voice. It's kind of funny.

His thread about a single flyer and a flash he caught on camera, and there being some sort of correlation is a good read too, lol.
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I still think wind is more of a factor of the flier, than 4fps change in MV. Unless you shooting a rail gun, or a braced gun, inside with no wind, in a 100% human error out of it. With the same cleanliness of barrel. You'll not gonna have 100% the same if doing it outside. I notice on my annie I do shave some lead on my bullets manually inserting.
 
_Shorty said:
grauhanen, powder does not all burn at the same rate. I don't know why you cannot understand that. It is a simple matter.
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This is not about propellant burn rates. Regardless of whether or not the small amount of the same kind of propellant in the same kind of .22LR match ammo round has a variety of burn rates, the fact remains that when two bullets go from 0 fps to the same MV in the same barrel they must do so in the same way, with the same acceleration. There are no "different acceleration curves" to affect the flight of different bullets as they go to the target.

If I'm wrong and there is such information demonstrating Shorty is correct, I welcome it. I prefer to admit a mistake and learn something.

I invite any reader or poster -- especially those who support Shorty -- to kindly do so. Please share reliable and verifiable sources of information which confirm his view that the same kind .22LR match rounds with the same MV will have what Shorty calls "different acceleration curves" -- or, to put it another way, different ways to get from 0 fps to the same muzzle velocity in the same barrel.

In the absence of reliable information to support his position, it may be reasonably taken that no reader or poster here is aware of any. Perhaps all can agree that in the absence of such information, nothing further needs to be added to this thread.
 
grauhanen said:
This is not about propellant burn rates. Regardless of whether or not the small amount of the same kind of propellant in the same kind of .22LR match ammo round has a variety of burn rates, the fact remains that when two bullets go from 0 fps to the same MV in the same barrel they must do so in the same way, with the same acceleration. There are no "different acceleration curves" to affect the flight of different bullets as they go to the target.

If I'm wrong and there is such information demonstrating Shorty is correct, I welcome it. I prefer to admit a mistake and learn something.

I invite any reader or poster -- especially those who support Shorty -- to kindly do so. Please share reliable and verifiable sources of information which confirm his view that the same kind .22LR match rounds with the same MV will have what Shorty calls "different acceleration curves" -- or, to put it another way, different ways to get from 0 fps to the same muzzle velocity in the same barrel.

In the absence of reliable information to support his position, it may be reasonably taken that no reader or poster here is aware of any. Perhaps all can agree that in the absence of such information, nothing further needs to be added to this thread.
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It most certainly is about propellant burn rates. The propellant burning is where the energy to accelerate comes from. No powder is 100% homogeneous. All of it, even within a single round's powder charge, is an imperfect mixture with imperfect shapes. The mixture affects burn rate. The shape affects burn rate. Every single kernel can burn faster/slower than the next one. Yes, the more consistent the mixture the more consistent the burn rate. But nothing is perfect. Again, I invite you to look at this pressure trace graph for seven different rounds that you seem to be conveniently ignoring:

uc


That is seven different shots that the guy attempted to load with exactly the same amount of powder. The only difference between the seven rounds was the bullet seating depth. The first three shots were loaded with the bullet out touching the lands, and the next four shots were loaded with the bullets 0.030" deeper into the case, so 0.030" further away from the lands than the first three. If powder burn rates were 100% consistent you would only see two lines. One line for the three touching rounds, and one line for the four 0.030" off rounds. You would not see seven distinct lines because all three of the touching rounds should all burn at exactly the same rate as each other, and so they should have pressure traces that exactly match each other. And the same goes for the four 0.030" off rounds. They should have a different curve than the touching rounds, but they should have the same curves as each other. So they should have lines that perfectly match each other, too. Not only that, but the lines should be perfectly smooth curves. They should not have those wiggles back and forth along their entire lengths. If the powder burned at a consistent rate those wiggles would not exist.

So why don't the three that are alike and the four that are alike have traces drawn exactly matching each other? Precisely because the powder burns at different rates within a single round's charge, as well as different from round to round. The three touching rounds have the higher pressure traces that breach 40,000 PSI. And the other four have the lower pressure traces that have much lower max pressures. The max pressures all differ from each other. And the overall curves all differ from each other. And they all wiggle like crazy. This is because the powder is burning at different rates the entire time each shot's powder is burning. Powder manufacturers do their best to make each lot of powder as homogeneous as possible, but that doesn't mean every single kernel is exactly like the next one. The better the powder the more consistent the burn rate will be, but nothing is perfect. There is always some variance. Better powders just have less variance. Less doesn't mean zero. It just means less. And that variance in burn rate means a variance in acceleration.

I really do not understand why you are so stuck on this idea that "The barrel is a fixed length so if the bullet exits at x velocity it must have exactly this prescribed acceleration from start to finish. There is no other way for it to have that speed when it only had that fixed amount of distance to get to that speed." This relies on assuming powder burns perfectly at one rate, and that isn't reality. Powder burning is imperfect. It's not like an airgun with a freshly filled tank that has a precise amount of air at a precise pressure to release all at once. The powder burns at a constantly changing rate to release gas at a constantly changing pressure which accelerates the bullet at a constantly changing rate. The more consistent that burn is the more consistent the end velocity will be. But if it were burning so consistently that it always had the same acceleration rate then why wouldn't it also always have precisely the same muzzle velocity? It's not a perfect release of energy. It varies. And not just in the amount of powder present, but varies in how that powder burns, too.

Why do tuners work then? This is just another example of something that isn't perfect. Tuners can help you reduce vertical. But because the ammo isn't perfect there is still some dispersion, even when the tuner has things dialled in as well as it can. That's why it can go from something like this:

uc


to something like this:

uc

(source: http://www.geoffrey-kolbe.com/articles/rimfire_accuracy/tuning_a_barrel.htm)

but you don't see 100-round "groups" the same size as a single bullet hole. Ammo varies, and thus even with a dialled-in tuner you're still going to have some dispersion. A 24" barrel only needs to move 0.007" for a 1 MOA "flier" to happen at 50 yards, don't forget. So on that tuned barrel when two shots are both 1085 fps but have slightly different exit times due to slightly different powder burn rates you get slightly different launch angles and a slightly different POI as a result. Tuners give you better results. They don't give you complete compensation. They can't, because ammo isn't perfect. It's why CCI Standard Velocity shot with a well-tuned barrel still shoots worse than Eley Tenex with a well-tuned barrel. The CCI has more variance to begin with, and the tuner can only help you so much. If the exit times for all shots were perfectly linear with their MV then a tuner would be able to provide perfect compensation for that difference in MV. But because the exit times have some variance to them you still get some dispersion. Not all 1085 fps shots are alike. Better ammo makes them more alike on average, but better ammo isn't perfect ammo.
 
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skwerl said:
I have always wondered how 2 drag race cars can have
the same ET (time) with different top speeds.

Does this explain it , partly ?
...skwerl
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Both drivers are sitting there waiting for the green lights, and floor it once they come on. Car A gets to the 60-foot line first, but Car B makes a little more horsepower up top, so while it was behind at the 60-foot line because it had less acceleration than Car A up to that point, it is now making more horsepower than the other car and accelerating more quickly now as a result. He gains and gains and it is virtually a tie at the line. Since he lost to the 60-foot line he was going slower than the other guy up to that point. So in order to reach the finish line at the same time as the other guy he's got to be going faster, because he had to make up the time he lost in the first half of the race. Same elapsed time at the finish line, but he's going faster than the other guy now after playing catch-up.

grauhanen, here's another interesting graph:

uc


(source: http://www.geoffrey-kolbe.com/articl...g_a_barrel.htm)

This shows the exit times from a tuner test. He used equipment to actually measure how much time there was from ignition to bullet exit, and as you can see, exit time is not directly related to MV. Velocity is on the x axis, so any green squares that line up vertically have the same MV. There are several examples where they have different exit times when their velocities are very similar. And you can also look for squares that line up horizontally and see how there were some shots with very similar exit times but very different velocities. This is happening because the powder is burning at different rates for each shot. The red line is the regression that he used to tune with, but the small amount of dispersion still seen in his tuned results is due to the fact that all the green squares aren't all perfectly on that red line. Your idea that all shots accelerate the same would mean that all the green squares were precisely on that red line. And it just doesn't happen that way.

I sure hope you don't think I'm just digging at you. I'm not. I'm just hoping that one of these times it finally clicks and you see what happens and why. In this case you do happen to be wrong, and I'm hoping for you to see the light, as it were. Powder simply does not burn perfectly the same every time. It burns a little differently all the time, even within a single charge. And that's a factor in all of these things being slightly different each time. Slightly different acceleration rates. Slightly different exit times. Slightly different launch angles. Slightly different POI. Tuners would work perfectly if power burn rates were 100% consistent. So even if the amount of powder in each case was slightly different, but the burn rate was 100% the same, then the tuner would be able to perfectly compensate for the MV difference and give you perfectly compensated launch angles every time, and you'd get single bullet hole groups except for the wind. But since powder isn't perfect, even tunnel testing exhibits some dispersion, because the tuner can't compensate for varying powder burn rate. It can only compensate perfectly for MV difference when the powder burn is impossibly consistent.
 
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_Shorty said:
Both drivers are sitting there waiting for the green lights, and floor it once they come on. Car A gets to the 60-foot line first, but Car B makes a little more horsepower up top, so while it was behind at the 60-foot line because it had less acceleration than Car A up to that point, it is now making more horsepower than the other car and accelerating more quickly now as a result. He gains and gains and it is virtually a tie at the line. Since he lost to the 60-foot line he was going slower than the other guy up to that point. So in order to reach the finish line at the same time as the other guy he's got to be going faster, because he had to make up the time he lost in the first half of the race. Same elapsed time at the finish line, but he's going faster than the other guy now after playing catch-up.
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Turbo cars are well known for that over the years , leaving the line softer with a harder top end charge.
 
Dont really think references to drag racers have much to do with a contained explosion that has no factors affected by human influence. Once in motion there is nothing we do that affects it! All this is intertesting but since we cant control,manipulate or change any of variables to produce an effect beneficial to shooting smaller groups. I respect how intelligent many of our members are on this site. Just curious how many have made the 1/4" club or posted more 1/2" at 50 groups or aggregates of 100 yard targets smaller than one of our members. Nobody is perfect but the proof is in his pudding. PUOSU
 
Longstud said:
Dont really think references to drag racers have much to do with a contained explosion that has no factors affected by human influence. Once in motion there is nothing we do that affects it! All this is intertesting but since we cant control,manipulate or change any of variables to produce an effect beneficial to shooting smaller groups. I respect how intelligent many of our members are on this site. Just curious how many have made the 1/4" club or posted more 1/2" at 50 groups or aggregates of 100 yard targets smaller than one of our members. Nobody is perfect but the proof is in his pudding. PUOSU
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Nothing wrong with trying to understand how things work. Drag racers don't accelerate at one fixed rate. Bullets don't accelerate at one fixed rate. People sometimes use analogies to try to illustrate concepts. They can help connect the dots. Whether or not one has control over the bullet acceleration isn't the point. The fact that the acceleration varies is the point. How might you try to teach someone that bullets don't accelerate at one fixed rate? Perhaps your method will bear more fruit.
 
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