Positive compensation or stopped muzzle, a more low tech test.
- Thread starter Dennis D.
- Start date
S
shooter65
Guest
I agree with everything you said but with the tuner settings at different distances. Once again...I have found a tuned barrel is a tuned barrel regardless of the distance.
A conversation between two other rimfire shooters. Just something to ponder on.....
Question:
After the Metric State Dave K was talking to Olaf about barrel vibrations. He was explaining that you want the bullet to exit at the top or the bottom of the vibration.
I have thought about that and wonder why it is always assumed that vibrations are vertical. If you have a free floating symmetrical barrel, firmly attached to an action by machine screws into a stock(which we just talked about) with the action having a big loading hole on one side only, with vibrations set off by a firing pin strike above barrel center, the powder "explosion" maybe moving the cartridge case back to the bolt with a big bump against unsymmetrical bolt lugs, and the bullet and powder gasses starting off from motionless, why would we figure all vibrations were vertical?
I would think that the proof would be in the many rest groups you have seen over the years. Our current ideal would be a nice round group that fit inside the c ring, but would not that even show the vibrations were not all vertical?
Assuming very good ammo(without case dents and bullet deformations!!!) when the barrel vibration is not exactly correct and the ideal small group is not seen, have you noted the groups are all strung vertical, or are they strung in different directions, showing vibrations in other than vertical directions?
Response:
Hopefully no one with a formal mathematics background will see this and try to punish me for over simplifying. Muzzle motion is normally quite evenly distributed in a polar sense (the bore axis being the polar axis) about the polar axis. My efforts involve diminishing the amplitude of the oscillations by increasing their frequency (assuming a constant amount of energy expended, amplitude is inversely proportional to frequency) and controlling the manner of the dissipation of that energy by stiffening and damping the system. If two accelerometers were attached to the muzzle, one to sense horizontal movement and the other vertical and their outputs connected to the x and y axes of an oscilloscope, one would likely observe a Lissajous pattern displayed which is the result of sinusoidal oscillations in both planes.
My observations support this kind of behavior.
A conversation between two other rimfire shooters. Just something to ponder on.....
Question:
After the Metric State Dave K was talking to Olaf about barrel vibrations. He was explaining that you want the bullet to exit at the top or the bottom of the vibration.
I have thought about that and wonder why it is always assumed that vibrations are vertical. If you have a free floating symmetrical barrel, firmly attached to an action by machine screws into a stock(which we just talked about) with the action having a big loading hole on one side only, with vibrations set off by a firing pin strike above barrel center, the powder "explosion" maybe moving the cartridge case back to the bolt with a big bump against unsymmetrical bolt lugs, and the bullet and powder gasses starting off from motionless, why would we figure all vibrations were vertical?
I would think that the proof would be in the many rest groups you have seen over the years. Our current ideal would be a nice round group that fit inside the c ring, but would not that even show the vibrations were not all vertical?
Assuming very good ammo(without case dents and bullet deformations!!!) when the barrel vibration is not exactly correct and the ideal small group is not seen, have you noted the groups are all strung vertical, or are they strung in different directions, showing vibrations in other than vertical directions?
Response:
Hopefully no one with a formal mathematics background will see this and try to punish me for over simplifying. Muzzle motion is normally quite evenly distributed in a polar sense (the bore axis being the polar axis) about the polar axis. My efforts involve diminishing the amplitude of the oscillations by increasing their frequency (assuming a constant amount of energy expended, amplitude is inversely proportional to frequency) and controlling the manner of the dissipation of that energy by stiffening and damping the system. If two accelerometers were attached to the muzzle, one to sense horizontal movement and the other vertical and their outputs connected to the x and y axes of an oscilloscope, one would likely observe a Lissajous pattern displayed which is the result of sinusoidal oscillations in both planes.
My observations support this kind of behavior.
M
mks
Guest
Seems like we are making some progress. Now let's go back to Varmint Al's graph that shows the trajectory of a slow and a fast bullet. For these two to strike the 50 yard target at the same elevation, the slow one has to be launched from the muzzle at a higher angle. It rises higher at midrange and when it gets to the target is still moving slower and falling at a greater angle than the faster bullet. The trajectories of the two bullets cross paths at 50 yards, and at increasing range beyond 50, the slower bullet falls farther and farther below the faster bullet.
Now if we wanted to, we could further increase the launch angle of the slow bullet so that both strike the 100 yard target at the same elevation. But then the slow bullet would have to be on a higher trajectory at shorter ranges than the fast bullet. Tuning for vertical dispersion due to muzzle velocity differences can only be perfect at one yardage.
So, you see, it just isn't possible for a rifle to be tuned for all distances with one setting of the tuner. Whether one can see the effects of tuning, with the wind pushing the bullet every which way, is another question. For a 50 yard tune, according to Al's calculations, the slower bullet strikes the target just 0.33" below the fast one at 100 yards. To find this difference takes measurements of a lot of shots of known velocity.
M
mks
Guest
For my 30BR, I have varied the powder charge by 2 grains in 0.2 grain increments, which gave me ES of about 150 fps. This window contained 2-3 nodes. The range of powder charge and increment can be varied depending on what you are looking for.
M
mks
Guest
Vibrations occur in the vertical, horizontal, longitudinal and torsional directions. Varmint Al's website shows vertical and longitudinal vibrational modes, but not horizontal and torsional, because the model is simplified to two dimensions. The reason we focus on vertical vibration is because it is typically the largest motion for a rifle with the bore significantly above its center of gravity.
No. This would only be true for rifles with the bore aligned with the center of gravity.
Some interesting concepts here that could be discussed at length. Smaller amplitude is better for all vibrational directions except vertical. For the vertical direction, more amplitude is needed for tuning of the typical rifle. Stiffness decreases amplitude, but has the disadvantage of increasing frequency, which can cause more motion to occur before bullet exit. Adding mass, on the other hand, decreases amplitude and frequency. Damping decreases amplitude without affecting frequency much. Stiffness and damping can be added asymmetrically, but asymmetrical mass is more difficult. The surface has barely been scratched on the potential for tuning the dynamics of a rifle.
The scientists at the Ballistics Research Lab have measured and published Lissajous-like patterns for cannons. Accelerometers aren't very useful for measuring barrel motion, because what matters is muzzle angle, not acceleration.
V
Varmint Al
Guest
mks, Very well stated. The FEA rifle dynamic calculations have a vertical plane of symmetry and therefore there is no horizontal motion allowed. Since gravity does not act horizontally there is not a horizontal compensating effect on accuracy like the vertical positive compensation. The mass of the tuner does decrease the amplitude of any horizontal muzzle motion which tends to decrease horizontal dispersion.
I did a full 3-D FEA calculation of the rifle with a loading port and bolt handle. I also included rifling in the barrel. The calculation too many hours to run on my base computer and the horizontal desperation was in the noise.
Good Hunting... from Varmint Al
M
mks
Guest
mks, Very well stated. The FEA rifle dynamic calculations have a vertical plane of symmetry and therefore there is no horizontal motion allowed. Since gravity does not act horizontally there is not a horizontal compensating effect on accuracy like the vertical positive compensation. The mass of the tuner does decrease the amplitude of any horizontal muzzle motion which tends to decrease horizontal dispersion.
I did a full 3-D FEA calculation of the rifle with a loading port and bolt handle. I also included rifling in the barrel. The calculation too many hours to run on my base computer and the horizontal desperation was in the noise.
Good Hunting... from Varmint Al
Al,
Good to hear about your latest results. I also noticed the barrel with flats top and bottom did some good. In the BRL measurements on a cannon barrel, it almost looks like torsional motion combined with vertical might be creating horizontal motion. I'm glad that isn't a significant factor in BR barrels. One less thing to worry about.
Cheers,
Keith
Keith, what happens when the center of mass in a rifle is in the same plane as the center of the bore? Let's assume the rifle is free to recoil -- not stopped by someone's shoulder. On your model, it would be untunable, right? Yet there is real-world evidence to the contrary, from 1,000 yard benchrest, where gravity always rears its head.
V
Varmint Al
Guest
Here is an experiment where the bore axis was inline with the recoil by design. With such a condition there was no force to change the muzzle's vertical pointing position. There was no positive or negative compensation. This was reasonably close to a fixed muzzle. See the experiment here:
http://www.border-barrels.com/articles/rimfire_accuracy/velocity_dispersion.htm
Good Hunting... from Varmint Al
Al, to prove a point, I've posted this link a few too many times in the past month, but I don't think you've seen it. The record was set several years ago, but we've found rifles constructed like the one shown here shoot round groups. Tuning just seems to expand or shrink the groups, but not to affect the characteristic shape.
Note that these are shot at 1,000 yards. Were the groups always round? No, of course not, wind and air movement over the terrain have an effect. But I'll stand by my statement, which has almost 10 years of testing behind it. Groups are round, even at 1,000 yards. Velocity ES is in the low double-digits.
(I know this one isn't perfectly round. It was shot at Bench 1 at Hawks Ridge, and there was always a bit of dispersion due to the terrain. There was a 100-foot gully, at an angle, between 500 to 1000 yards. There was a shallower gully, still a fair bit wide, before 500 yards. The air near the ground is like the water next to the river bank.)
http://bulletin.accurateshooter.com...ets-new-ibs-1000-yard-heavy-gun-world-record/
Thoughts?
Note that these are shot at 1,000 yards. Were the groups always round? No, of course not, wind and air movement over the terrain have an effect. But I'll stand by my statement, which has almost 10 years of testing behind it. Groups are round, even at 1,000 yards. Velocity ES is in the low double-digits.
(I know this one isn't perfectly round. It was shot at Bench 1 at Hawks Ridge, and there was always a bit of dispersion due to the terrain. There was a 100-foot gully, at an angle, between 500 to 1000 yards. There was a shallower gully, still a fair bit wide, before 500 yards. The air near the ground is like the water next to the river bank.)
http://bulletin.accurateshooter.com...ets-new-ibs-1000-yard-heavy-gun-world-record/
Thoughts?
M
mks
Guest
Charles,
Yes, the rifle would be untunable if the bore is aligned with the center of mass, and the stiffness of all the parts is also symmetrical around the bore. Well, except that gravity can cause a little misalignment. Drag on the rests that is not in the same plane as the bore also would cause vertical. But these should be small effects compared to the typical CG offset.
Has the CG of Joel's rifle been measured? It looks like it is above the bore, which would induce tunable vertical just the same as below the bore.
Keith
Keith, yes, Joel's rifle (now mine, by the way) has a center of mass slightly above the boreline. He had an earlier one that was the same, with which he won, no kidding, about half the HG matches at Hawks Ridge for a 2-year period.
I have a similar rifle, but the bit of extra weight is below the boreline. This is the second of that configuration. Before that, I had a rather conventional HG (stock a 50-cal McMillan). All won more than my meager talents would have forecast.
Two Australian shooters, Tonz Z and Jeff Rogers have tensioned barrel riles, of a more conventional design (most weight below boreline). I think Tony Z does well; Jeff has a number of Australian records.
All these rifles shoot the round-group pattern. All respond a bit to load changes, i.e., tuning, but not in the "changing group shape" mode.
I have had two barrel-tensioned Light Guns (17-pound max weight) that did change group shape. I do not know why, as I have also had 2 that shot the characteristic round group. I believe it was due to heat, but am not sure.
What I'm trying to suggest is not that the conventional analysis is wrong, but only a part of the story. To satisfy me, a model is going to have to account for the round-group characteristic of the big, heavy-tube rifles. Before dismissing this, I believe Vaughn himself allowed that as a barrel approached 3 inches in diameter, it also began to not be affected by harmonics.
I also seem to remember reading about an unlimited rimfire that was built along these lines (don't remember whether or not the barrel was under tension). This was in Precision Shooting some years ago -- wish I could remember the volume/issue.
We've had a couple of people (not you) who got quite angry when empirical results did not fit a model. This with the "when the humidity drops, N-133 is affected" tale. Much gnashing of teeth. Humidity does not affect gunpowder, according to Henry Child's model. Now Henry is a good man, and has done a lot of worthwhile testing on rifles. But the results with N-133 were repeatable. When empirical evidence does not agree with the model, the exception has to be explained, not dismissed.
All help, esp. by such talented people, gratefully accepted.
I have a similar rifle, but the bit of extra weight is below the boreline. This is the second of that configuration. Before that, I had a rather conventional HG (stock a 50-cal McMillan). All won more than my meager talents would have forecast.
Two Australian shooters, Tonz Z and Jeff Rogers have tensioned barrel riles, of a more conventional design (most weight below boreline). I think Tony Z does well; Jeff has a number of Australian records.
All these rifles shoot the round-group pattern. All respond a bit to load changes, i.e., tuning, but not in the "changing group shape" mode.
I have had two barrel-tensioned Light Guns (17-pound max weight) that did change group shape. I do not know why, as I have also had 2 that shot the characteristic round group. I believe it was due to heat, but am not sure.
What I'm trying to suggest is not that the conventional analysis is wrong, but only a part of the story. To satisfy me, a model is going to have to account for the round-group characteristic of the big, heavy-tube rifles. Before dismissing this, I believe Vaughn himself allowed that as a barrel approached 3 inches in diameter, it also began to not be affected by harmonics.
I also seem to remember reading about an unlimited rimfire that was built along these lines (don't remember whether or not the barrel was under tension). This was in Precision Shooting some years ago -- wish I could remember the volume/issue.
We've had a couple of people (not you) who got quite angry when empirical results did not fit a model. This with the "when the humidity drops, N-133 is affected" tale. Much gnashing of teeth. Humidity does not affect gunpowder, according to Henry Child's model. Now Henry is a good man, and has done a lot of worthwhile testing on rifles. But the results with N-133 were repeatable. When empirical evidence does not agree with the model, the exception has to be explained, not dismissed.
All help, esp. by such talented people, gratefully accepted.
S
shooter65
Guest
Some additional thoughts....
I will tell you some of my ideas on high power rifle barrel vibrations and what we worked on for 1,000 yard accuracy. A .308 round for 1,000 yards, back when I was shooting in the '80's used a 190, 200 or 210 grain bullet at about 70,000 pressure. This is quite different from a .22 long rifle match round with a 40 grain bullet at about 10,000 pressure. However, there might be some correlations.
In any cartridge case, no matter how well made, there is a thin side and a thick side. In .308 the minimum difference on really good match cases that were sorted after wall measurement was .001". Usually a lot more, and in Mil cases really a lot more.
When the round fires, the primer ignition pushes the case forward, the primer partially coming back out of the case, the base of the case then slams back onto the bolt head and the primer completely reseated again when the powder ignites and builds up pressure*. The thin side of the case lengthens more than the thick side, so the base at the thin side hits the bolt head first. If the thin side is randomly placed in the chamber, the case head hits on different sides of the bolt head and sets up different vibrations which then travel out onto the long barrel. The cases then assume a banana shape(really very small), so when they are reloaded and placed in random ways in the chamber, they are not really centered.
To control that we would measure the case wall thickness of all the match cases, select the ones with the minimum difference, and mark either the thin side or thick side with a small notch filed on the case head. These cases were never full length sized, only neck sized enough to hold the bullet. Each time the round was loaded, single loading for long range slow fire, the notch was always in the same up position. This, hopefully, then produced the same vibration when fired. However, by not full length sizing, the case pretty much filled the chamber and was already pushed up against the bolt face, eliminating most of the case striking the face of the bolt. However, some believe the primer had enough force to push the case into the chamber enough to slightly move the shoulder back, then the case would still bang back onto the bolt face.
In the usual high power bolt rifle there are two bolt lugs and when the bolt is closed, the lugs are at 12 and 6 o'clock. The Palma shooters have developed the 4 lug bolt, the lugs carefully machined and lapped to all lock up the same(production bolts never do, even 2 lug bolts). If a case has the thin and thick sides at 3 or 9 o'clock, in the 2 lug bolt, it causes a lot more vibration than if the case was at 6 or 12. With the 4 lug bolt, the shooters do not have to worry as much about how the case is put into the chamber. However, I would think there would still be some variation even when there are 4 lugs if the cases were inserted randomly.
Back to smallbore - We have no way of measuring case wall variations. Maybe there is not enough pressure to stretch the case, thick or thin side. When I started SB I did everything - measure case rims, etc. From that I noticed that the rims were usually not flat in the measuring device, in other words not 90 degrees to the case wall, meaning even if they did not stretch, one side of the rim hit the bolt head first in a random pattern.
With SB barrels as heavy as high power barrels, maybe the very small firing impact and long time of the bullet in the barrel, allows the barrel back to neutral where it started before the round fired by the time the bullet reaches the muzzle. Keep in mind, a .22 round reaches maximum velocity at about 16-18 inches of the barrel, and slows down after that because friction over comes powder pressure until it exits the barrel.
So, would the position of the firing pin make a difference if it were on the top or bottom or both the top and bottom, or maybe even better at 12, 3, 6 and 9 o'clock. The firing pin hits the case and moves the case forward a bit. The case then pushes back against the bolt head. With our tight chambers and the lead bullet jamming the lands, does the case really move forward much so that it has to bang back, causing vibrations? If it does would the buildup of bullet lube between the case and the bolt face cause this impact to vary during a long match? Does the mouth of the .22 case against the front of the chamber help hold the case back as should the shoulder of the bottle neck case, or is there tolerance there as in the bottle neck chamber?
Perhaps electronic ignition as in some artillery rounds would make a difference since the firing pin impact would not be there. As a general thought, if Anschutz is not worried about this, should we be?
*If you have ever fired very light loads in a centerfire gun, you probably noticed the primers after firing were sticking out of the head of the case some. The primer ignition pushed the case forward against the shoulder of the chamber with the primer only backing up to the bolt head, and the powder pressure of the light load not enough to push the case back against the bolt head and reseat the primer.
I will tell you some of my ideas on high power rifle barrel vibrations and what we worked on for 1,000 yard accuracy. A .308 round for 1,000 yards, back when I was shooting in the '80's used a 190, 200 or 210 grain bullet at about 70,000 pressure. This is quite different from a .22 long rifle match round with a 40 grain bullet at about 10,000 pressure. However, there might be some correlations.
In any cartridge case, no matter how well made, there is a thin side and a thick side. In .308 the minimum difference on really good match cases that were sorted after wall measurement was .001". Usually a lot more, and in Mil cases really a lot more.
When the round fires, the primer ignition pushes the case forward, the primer partially coming back out of the case, the base of the case then slams back onto the bolt head and the primer completely reseated again when the powder ignites and builds up pressure*. The thin side of the case lengthens more than the thick side, so the base at the thin side hits the bolt head first. If the thin side is randomly placed in the chamber, the case head hits on different sides of the bolt head and sets up different vibrations which then travel out onto the long barrel. The cases then assume a banana shape(really very small), so when they are reloaded and placed in random ways in the chamber, they are not really centered.
To control that we would measure the case wall thickness of all the match cases, select the ones with the minimum difference, and mark either the thin side or thick side with a small notch filed on the case head. These cases were never full length sized, only neck sized enough to hold the bullet. Each time the round was loaded, single loading for long range slow fire, the notch was always in the same up position. This, hopefully, then produced the same vibration when fired. However, by not full length sizing, the case pretty much filled the chamber and was already pushed up against the bolt face, eliminating most of the case striking the face of the bolt. However, some believe the primer had enough force to push the case into the chamber enough to slightly move the shoulder back, then the case would still bang back onto the bolt face.
In the usual high power bolt rifle there are two bolt lugs and when the bolt is closed, the lugs are at 12 and 6 o'clock. The Palma shooters have developed the 4 lug bolt, the lugs carefully machined and lapped to all lock up the same(production bolts never do, even 2 lug bolts). If a case has the thin and thick sides at 3 or 9 o'clock, in the 2 lug bolt, it causes a lot more vibration than if the case was at 6 or 12. With the 4 lug bolt, the shooters do not have to worry as much about how the case is put into the chamber. However, I would think there would still be some variation even when there are 4 lugs if the cases were inserted randomly.
Back to smallbore - We have no way of measuring case wall variations. Maybe there is not enough pressure to stretch the case, thick or thin side. When I started SB I did everything - measure case rims, etc. From that I noticed that the rims were usually not flat in the measuring device, in other words not 90 degrees to the case wall, meaning even if they did not stretch, one side of the rim hit the bolt head first in a random pattern.
With SB barrels as heavy as high power barrels, maybe the very small firing impact and long time of the bullet in the barrel, allows the barrel back to neutral where it started before the round fired by the time the bullet reaches the muzzle. Keep in mind, a .22 round reaches maximum velocity at about 16-18 inches of the barrel, and slows down after that because friction over comes powder pressure until it exits the barrel.
So, would the position of the firing pin make a difference if it were on the top or bottom or both the top and bottom, or maybe even better at 12, 3, 6 and 9 o'clock. The firing pin hits the case and moves the case forward a bit. The case then pushes back against the bolt head. With our tight chambers and the lead bullet jamming the lands, does the case really move forward much so that it has to bang back, causing vibrations? If it does would the buildup of bullet lube between the case and the bolt face cause this impact to vary during a long match? Does the mouth of the .22 case against the front of the chamber help hold the case back as should the shoulder of the bottle neck case, or is there tolerance there as in the bottle neck chamber?
Perhaps electronic ignition as in some artillery rounds would make a difference since the firing pin impact would not be there. As a general thought, if Anschutz is not worried about this, should we be?
*If you have ever fired very light loads in a centerfire gun, you probably noticed the primers after firing were sticking out of the head of the case some. The primer ignition pushed the case forward against the shoulder of the chamber with the primer only backing up to the bolt head, and the powder pressure of the light load not enough to push the case back against the bolt head and reseat the primer.
M
mks
Guest
Round groups don't necessarily mean that the gun is tuned. Some possible cases are: 1. no wind + perfect tune and/or low ES = round groups, 2. no wind + imperfect tune and higher ES = vertical groups, 3. some wind + perfect tune and/or low ES = horizontal groups, 3. some wind + imperfect tune and higher ES = round groups. The main point is that low ES can substitute for tune in decreasing vertical. At 1000 yards with BC = 0.6 and ES = 10, the vertical with no compensation is only about 1.6". That is about how much Joel's group is taller than wide. So it's possible that the gun isn't tuned at all, but just had low ES on those ten shots.
Have you ever shot large ES on purpose with this gun just to test whether it is tuned?
Uh, no, I've shot them by accident trying to find a load. This would be at 100 yards, and yes, they're still round, IIRC. But not the sort of thing that shows much at 100. When I find a good load at 100, if it has a bullet hole or more of vertical, I asterisk it until I've fired a few 1K matches, to make sure the 100 yard test results carry over to 1,000.
Remember, we've been using these in competition for over 10 years now. The bulk of the data collected is in the form of "wins," with occasional numbers coming from testing.
On the other hand, given the improvement in 1K guns generally over the past 15 years, it is data that can't be ignored. I wish Jeff Rodgers or Tony Z would chime in, Tony may actually have data in the form engineers like.
I think all of us would settle for a vertical dispersion of 1.6 inches at 1K, and most people would settle for .16 at 100 yards (and 0.08 at 50 yards). Don't RF rifles keep ES to about 10? Even if it is 20, we're talking about the size of the x-ring, right? Why are we working on this if things are that small?
It is guys with 15 inches at 1,000 that go back to testing. But remember B.C. too is not a single number for a kind of bullet; people seem surprised to find there is a SD and ES for bullets. I've seen ES of .020 for a popular commercial .30 caliber. And (again IIRC), that's worth about 4 inches at 1,000 yards. Probably not a big factor in RF, your TOF isn't measured in full seconds.
A lot, and I mean quite a lot of match rimfire ammo has an ES of a good 25-30 fps. Some of the truly great stuff I've shot has been in the 4-7 fps range for what that's worth.
HuskerP7M8
Member
Charles,
I use two CED M2 chronographs that I’ve calibrated to match each other and I’ve modified the screen spacing to 10’ from the original 2’ factory setting. Both are converted to IR and they’re mounted upside-down to eliminate extraneous light sources.
In the last two years every single shot I’ve fired in my tunnel (maybe 20,000 rds?) has passed thru my chrono screens and has been located on target as a Cartesian Plane x,y coordinate with an accuracy of a few 0.001’s of an inch.
The majority of those rds have been high quality match ammo consisting of Eley Tenex, Match, and Team as well as Lapua X-act, Midas, and Center X. I’m just guessing off the top of my head but probably at least 50 different lot #’s are included in this assortment of ammo.
The point I’m trying to make is that contrary to what you hear on internet forums, the chances of finding rimfire ammo with less than a 25 fps ES or SD’s in the mid to low single digits is difficult if not impossible with the 50 shot samples necessary to accurately generate those numbers. I suppose I could be incredibly unlucky and haven’t yet come across better ammo, but I’m sticking with those numbers at present.
You also mentioned that the ES of rimfire ammo might not be significant at the target, but if the average ES of most decent match ammo is in the 30 fps range…..a neutrally compensated barrel will cause approximately 0.21” of vertical dispersion at 50 yds and that’s not acceptable.
Landy
I use two CED M2 chronographs that I’ve calibrated to match each other and I’ve modified the screen spacing to 10’ from the original 2’ factory setting. Both are converted to IR and they’re mounted upside-down to eliminate extraneous light sources.
In the last two years every single shot I’ve fired in my tunnel (maybe 20,000 rds?) has passed thru my chrono screens and has been located on target as a Cartesian Plane x,y coordinate with an accuracy of a few 0.001’s of an inch.
The majority of those rds have been high quality match ammo consisting of Eley Tenex, Match, and Team as well as Lapua X-act, Midas, and Center X. I’m just guessing off the top of my head but probably at least 50 different lot #’s are included in this assortment of ammo.
The point I’m trying to make is that contrary to what you hear on internet forums, the chances of finding rimfire ammo with less than a 25 fps ES or SD’s in the mid to low single digits is difficult if not impossible with the 50 shot samples necessary to accurately generate those numbers. I suppose I could be incredibly unlucky and haven’t yet come across better ammo, but I’m sticking with those numbers at present.
You also mentioned that the ES of rimfire ammo might not be significant at the target, but if the average ES of most decent match ammo is in the 30 fps range…..a neutrally compensated barrel will cause approximately 0.21” of vertical dispersion at 50 yds and that’s not acceptable.
Landy