...except VM is mounted vertically and springer (Cometa 400) is hand held. Forearm of the rifle was supported near the balance point with the left hand. Right hand on the grip maintained very light contact with right shoulder for "artillery," pulled it in tight for "firm."
First plot is transverse velocity of muzzle. Note very low value at pellet exit (exit indicated by red trace) for both holds. ~0.1m/s = ~0.3fps = ~0.4mrad = ~1.3MOA
Second plot is transverse displacement (integral of velocity). Note similar values at pellet exit. They differ by only about 0.1mm = ~0.7MOA. Honestly, I expected more.
Please note velocity plot (top) is inverted (sorry about the inconsistency). Oops. I also just noticed that I forgot to apply the appropriate volts-to-m/s calibration constant in the more recent plots, so they overstate the actual quantitative motions (relative to the "rug" shot, which was properly calibrated) by ~60%. My excuse was that I was kind of excited about posting them and the calibration error doesn't affect relative comparison of "firm" to "artillery."
Sorry that I haven't been able to make myself clear Steve:
I would like to see a SUPERPOSED images because it is hard to compare things when they are isolated from each other.
It SEEMS to be that the "Artillery hold" pushes the pellet exit about half a ms later, but without superposing the plots its hard to see.
It also SEEMS that a few tenths of ms error on the "walk back" of the pellet exit time to the real exit time point could create problems in our understanding. If you look at the "Firm Hold" plot of TMV (Transverse Muzzle Velocity), the plot seems to be going from an area of relatively high TMV towards an area of relative calm, whereas if we look at the "Artillery Hold" plot there is a strong re-bound where after a few tenths of a ms, the velocity goes south again, strongly. In the chart you show just above, the TMV is starting from a bad condition and getting substantially worse just after, so that a delay in the pellet exit would have have a rather large effect.
Remember that what I am trying to get at here is how "sensitive" the POI is to SMALL CHANGES of MV, and for that, we need to look at points where the TMV is close to zero.
It doesn't really matter what the muzzle's position is, what matters is what is its velocity (and in real life, we should be looking at both planes: XZ and XY). I would maintain that the smooth curve you show for the displacement is a mathematical figment. IT CANNOT be that smooth, so reverting to the RELIABILITY OF THE BASIC QUANTITY MEASURED principle, let's look at the velocities, and try to figure out what needs to be done to achieve a pellet exit at the best of times: when the TMV is as close to zero as possible.
For numerology's sake (and assuming I didn't make a mistake):
For a spring gun having an MV of 890 ± 9 fps (good tune, single digit SD), the max MV would be about 917 fps, and the min would be 863 fps.
Under these conditions, assuming a 16" barrel, linear acceleration and zero for V0 (all big assumptions), the shortest Barrel Time (BT) would be 2.91 ms, the longest BT would be 3.09 ms, or about 1/5th of a ms difference.
IF the MV is the same for both holds (somewhat questionable assumption), AND the plots are correct in the pellet exit time, then the gun should be slightly more accurate with a firm hold than with an artillery hold.
And let me remind you that experience with springers tells me that the best point of support is NOT the CoG but forward of that, sometimes considerably forward of that.
Of course it could be that the system is, up to a point, self correcting and when the MV is lower, the TMV is also lower, but without some "sample" and average + sSd curves, it is hard to think of all the possibilities.
As a gunsmith, I have always preferred to go in steps:
1.- Find the best pellet
2,- Find the best lube (Sometimes, repeat #1 to settle the matter)
3.- Find the most accurate velocity for the above defined projectile
4.- Tune the vibrations to that.
It is a long and hard process, but in the end you are usually rewarded by good performances. Few shooters understand this anyway, LOL!
Again, sorry for not making myself clear, and thanks for the effort and hard work.
Sorry that I haven't been able to make myself clear Steve:
I would like to see a SUPERPOSED images because it is hard to compare things when they are isolated from each other.
It SEEMS to be that the "Artillery hold" pushes the pellet exit about half a ms later, but without superposing the plots its hard to see.
It also SEEMS that a few tenths of ms error on the "walk back" of the pellet exit time to the real exit time point could create problems in our understanding. If you look at the "Firm Hold" plot of TMV (Transverse Muzzle Velocity), the plot seems to be going from an area of relatively high TMV towards an area of relative calm, whereas if we look at the "Artillery Hold" plot there is a strong re-bound where after a few tenths of a ms, the velocity goes south again, strongly. In the chart you show just above, the TMV is starting from a bad condition and getting substantially worse just after, so that a delay in the pellet exit would have have a rather large effect.
Remember that what I am trying to get at here is how "sensitive" the POI is to SMALL CHANGES of MV, and for that, we need to look at points where the TMV is close to zero.
It doesn't really matter what the muzzle's position is, what matters is what is its velocity (and in real life, we should be looking at both planes: XZ and XY). I would maintain that the smooth curve you show for the displacement is a mathematical figment. IT CANNOT be that smooth, so reverting to the RELIABILITY OF THE BASIC QUANTITY MEASURED principle, let's look at the velocities, and try to figure out what needs to be done to achieve a pellet exit at the best of times: when the TMV is as close to zero as possible.
For numerology's sake (and assuming I didn't make a mistake):
For a spring gun having an MV of 890 ± 9 fps (good tune, single digit SD), the max MV would be about 917 fps, and the min would be 863 fps.
Under these conditions, assuming a 16" barrel, linear acceleration and zero for V0 (all big assumptions), the shortest Barrel Time (BT) would be 2.91 ms, the longest BT would be 3.09 ms, or about 1/5th of a ms difference.
IF the MV is the same for both holds (somewhat questionable assumption), AND the plots are correct in the pellet exit time, then the gun should be slightly more accurate with a firm hold than with an artillery hold.
And let me remind you that experience with springers tells me that the best point of support is NOT the CoG but forward of that, sometimes considerably forward of that.
Of course it could be that the system is, up to a point, self correcting and when the MV is lower, the TMV is also lower, but without some "sample" and average + sSd curves, it is hard to think of all the possibilities.
As a gunsmith, I have always preferred to go in steps:
1.- Find the best pellet
2,- Find the best lube (Sometimes, repeat #1 to settle the matter)
3.- Find the most accurate velocity for the above defined projectile
4.- Tune the vibrations to that.
It is a long and hard process, but in the end you are usually rewarded by good performances. Few shooters understand this anyway, LOL!
Again, sorry for not making myself clear, and thanks for the effort and hard work.
HM
Sorry for the misunderstanding. Here you go. Red = firm, blue = rug. Velocity on top, displacement below.
If there are apparent differences in pellet exit times, they're likely due to a change in the location of the acoustic backstop impact sensor necessary in the hand-held tests.
Upon further reflection, I now suspect that in the hand-held experiments, the relocated pellet-exit sensor wasn't properly selectively responding to pellet impact against the backstop, but also to mechanical noise coming from the gun's action. The latter seems to have preceded the former by as much as a full millisecond.
The timing for pellet exit it shows is therefore unreliable. Please disregard.
Great way of looking at complicated phenomena distilled down to two variables.
I understand the limitations of light gates being put too close to the muzzle, but I think the microphone may be giving us the same problems. I still remember when the screens in chronographs were tapes made of a copper "wigglies" that got broken when the projectiles passed. Then got reset for every shot. And having to balance the cost of shooting the supports if you wanted to skimp on the length of the tape you used for each shot, ROFL! Long time ago, and we have moved forwards enormously!
Thanks again for your very special "eye" in these things.
NOW, EVEN IF the pellet exit was to be off by 1 ms, what intrigues me from this gun is that from ms 13 to ms 16 with the firm hold, the position of the muzzle does not seem to change much, as well as the TMV's seem to be close to zero, which would be an interesting point to "shot for" the pellet exit. 😉
Did you notice a curious feature present in the dynamics of all three "holds?" I refer to the reversal of muzzle recoil direction that occurs at ~2.5ms.
Initially we see a smidgeon of depression while the piston is presumably traversing roughly the first inch or so of stroke, then (more dominant) elevation begins. I wonder what's causing that initial wrong-way-wiggle.
Maybe there's a clue in the fact that it seems largest with a "firm" hold, smallest with "artillery."
@steve-in-nc One possibility is the piston starts to accelerate forward, the rifle wants to rotate, but the inertia of the barrel resists, so the barrel flexes, starting at the rear, causing the muzzle to fall minutely.
@steve-in-nc One possibility is the piston starts to accelerate forward, the rifle wants to rotate, but the inertia of the barrel resists, so the barrel flexes, starting at the rear, causing the muzzle to fall minutely.
Interesting. Also, since a breakbarrel is the subject in question, the breech pivot lockup may be playing a role.
As I recall (I'll go verify this shortly), the Cometa uses a spring loaded ball bearing as the detent.
As I recall (I'll go verify this shortly), the Cometa uses a spring loaded ball bearing as the detent.
Yup. Dozens (100s? 1000s?) of looks at the Cometa breech (once for every loading) made the detail memorable. Its lockup consists of a spring loaded ball in the breech block that snaps over the conical tip of a stud carried by the tube. Seems to work well enough.
However, I suddenly think Jim's on a better track with his thinking about inertia of different components of the gun "resisting" acceleration differently. Specifically, my suspicious eye is turning toward the stock and the elasticity of its wooden connection to the steel of the action.
Consider that its the center of mass of the stock that lies below the centerline of the piston's acceleration and is therefore responsible for the dominant reactive torque that causes recoil to elevate the muzzle. The CM of the action itself however, due to the location of the heavy breech and barrel, lies above centerline and so generates reactive torque that tends to depress the muzzle.
So...
Suppose momentary (i.e. "momentary" being 2.5ms = 1/400th of a second) "give" in the connection between action and stock is allowing the inertia of the action to be dominant at the beginning of recoil, thus causing our wrong-way-wiggle? Only later does the wood "catch up" and assert its dominant weight into the recoil reaction torque equation.
Thanks, Jim!
Now to try and figure out how/if that works to explain the effect of different holds.
I posted the following on John's thread on the (UK) Shooting the Breeze forum some nineteen days ago.
I attached an accelerometer to the muzzle of a break barrel, and recorded the muzzle vibration with the rifle sitting upside down, free to slide (kinetic friction ~2N) in a fixed cradle that prevented the rifle from rotating during the shot cycle. The first mode vibration turned out to be the reciprocal of the compression stroke time in milliseconds, so a nine millisecond compression stroke produced vibration frequency of 1000/9, or 111 Hz.
This is where we enter the unknown. It seems likely that the vibration recorded above combines with vibration resulting from the behaviour of the barrel due to the rotation of the rifle about the centre of gravity. When the breech block starts to rise due to the rotation of the rifle, the inertia of the muzzle will resist movement to some extent (depending on the stiffness of the barrel and whether mass has been added to the muzzle) until the force from the breech block overcomes any strain energy that's built up in the barrel, and it is quite feasible that, during this short period, the muzzle angle falls. Of course, the strain energy will convert to kinetic energy as the muzzle starts to rise (which may start the higher frequency vibration while the pellet is in the barrel as recorded by John) and, at piston stop, the momentum of the muzzle will keep it rising after the breech block has stopped, converting all the kinetic energy into strain energy. The muzzle is now probably pointing at a steeper angle than the rest of the barrel, and vibrating at far greater than 111 Hz.
As the breech block starts to fall, it initially adds even more strain energy to the barrel, so the muzzle possibly points even higher, until the force at the breech block overcomes the strain energy, and the angle of the muzzle starts to fall, and all of this activity will be adding to and/or modifying vibrations. It's around this point that the pellet exits, and only John's experiment can tell us where the muzzle is actually pointing throughout the recoil cycle, and at the precise point of pellet exit.
I posted the following on John's thread on the (UK) Shooting the Breeze forum some nineteen days ago.
...It seems likely that the vibration recorded above...
"...the vibration recorded above..."
This seems to imply that one of your lovely and highly illuminating graphs accompanied your text in the Brit-side post, of which we are bereft. You know Jim, they say if you didn't take a picture, it never happened.
I posted the following on John's thread on the (UK) Shooting the Breeze forum some nineteen days ago.
I attached an accelerometer to the muzzle of a break barrel, and recorded the muzzle vibration with the rifle sitting upside down, free to slide (kinetic friction ~2N) in a fixed cradle that prevented the rifle from rotating during the shot cycle
Jim,
Did this "fixed cradle" differ from the one you use for VM experiments where the rifle is cradled by wooden supports lined with short-pile carpet?
Otherwise, wouldn't the resilience of wood and carpet allow at least some rotation around the CM? Please note that the peak amplitude of the WWW is only a couple of hundred micrometers, and that was measured at the end of the lever arm furnished by the barrel.
I just realized I blithely typed that without really thinking about what it says about how incredibly good these VM thingies are. 200um = 0.008" = roughly twice the thickness of a typical sheet of paper, measured on the fly in fractions of a millisecond.
I THINK that the wood's elasticity is too small to create that "post-sear-break-microsurge" (since we are calling the rearwards facing movement recoil and the forwards facing movement surge, this is, in fact a small surge that happens just before the recoil, that then gives way to the big surge, IF I got my terminology right).
IF we explore that avenue, perhaps some comment of a first approach to tuning a breakbarrel with three stock screws works: The action is not PERFECTLY bedded into the stock. Some stocks have more inside curve than others, some have convex curves, some have concave curves. MOST break-barrel airguns respond well to a "Stock" tune, where you tighten the REAR stock screw to about 27 in-lbs, and the front stock screws (usually in the forearm) are tightened to 10 in-lbs. Some groups are then fired, and the torque in the front stock screws is increased by about in-lbs, the process is repeated till you find the "sweet spot" of torques for that gun. IF the stock has not been completely sealed (as happens often with Walnut stocks that finished to be "pretty" with oil derivatives), then when the humidity changes, the procedure needs to be repeated. Underlever rifles of the same architecture (3 stock screws) usually respond well, though not as dramatically as the breakbarrels.
So, this shows that the "intensity" of vibrations produced by the shot cycle depends on the "quality" of the contact between action and stock, more than on the elasticity of the stock itself.
It is also a reason why Beech stocks are BETTER for spring-piston airguns than Walnut.
Now, thinking a bit differently, and this is only my theory:
That micro-surge has to come from the action of the spring & piston, and in THIS particular example, I would attribute it to the "drag" created by the piston seal when the pressure climbs enough to expand the parachute seal and therefore from the initial, low friction condition (good tuners size their seals to a resistance/drag between piston and compression chamber not higher than 1½-2 # with no pressure), the situation changes to a high drag condition where the seal is being squished against the sides of the compression chamber and therefore the action of the piston drags the whole gun forward.
As soon as the pressure reaches pellet release and the pressure-spring force reaches equilibrium, this again reverts to the normal "recoil" we feel.
From there on, the piston is pushing against a constant friction, pressure builds up because the pellet is still moving much slower than the pressure build-up, and the rest of the shot cycle is pretty much what we picture in our minds to be.
The ONLY way to prove/dispel this theory would be to test a rifle with two different pistons that have been "gauged" to produce the same pressure-free friction: one parachute sealed, the other ORing sealed. IF my theory is correct, and depending on how the gland for the ORing has been cut, the micro-surge would be HIGHER in the ORing sealed piston.
Of course, I may also be wrong.
😉
One more "Kudos to Jim!" from my side (and I am sure from John's as well).
I THINK that the wood's elasticity is too small to create that "post-sear-break-microsurge" (since we are calling the rearwards facing movement recoil and the forwards facing movement surge, this is, in fact a small surge that happens just before the recoil, that then gives way to the big surge, IF I got my terminology right).
IF we explore that avenue, perhaps some comment of a first approach to tuning a breakbarrel with three stock screws works: The action is not PERFECTLY bedded into the stock. Some stocks have more inside curve than others, some have convex curves, some have concave curves. MOST break-barrel airguns respond well to a "Stock" tune, where you tighten the REAR stock screw to about 27 in-lbs, and the front stock screws (usually in the forearm) are tightened to 10 in-lbs. Some groups are then fired, and the torque in the front stock screws is increased by about in-lbs, the process is repeated till you find the "sweet spot" of torques for that gun. IF the stock has not been completely sealed (as happens often with Walnut stocks that finished to be "pretty" with oil derivatives), then when the humidity changes, the procedure needs to be repeated. Underlever rifles of the same architecture (3 stock screws) usually respond well, though not as dramatically as the breakbarrels.
So, this shows that the "intensity" of vibrations produced by the shot cycle depends on the "quality" of the contact between action and stock, more than on the elasticity of the stock itself.
It is also a reason why Beech stocks are BETTER for spring-piston airguns than Walnut.
Now, thinking a bit differently, and this is only my theory:
That micro-surge has to come from the action of the spring & piston, and in THIS particular example, I would attribute it to the "drag" created by the piston seal when the pressure climbs enough to expand the parachute seal and therefore from the initial, low friction condition (good tuners size their seals to a resistance/drag between piston and compression chamber not higher than 1½-2 # with no pressure), the situation changes to a high drag condition where the seal is being squished against the sides of the compression chamber and therefore the action of the piston drags the whole gun forward.
As soon as the pressure reaches pellet release and the pressure-spring force reaches equilibrium, this again reverts to the normal "recoil" we feel.
From there on, the piston is pushing against a constant friction, pressure builds up because the pellet is still moving much slower than the pressure build-up, and the rest of the shot cycle is pretty much what we picture in our minds to be.
The ONLY way to prove/dispel this theory would be to test a rifle with two different pistons that have been "gauged" to produce the same pressure-free friction: one parachute sealed, the other ORing sealed. IF my theory is correct, and depending on how the gland for the ORing has been cut, the micro-surge would be HIGHER in the ORing sealed piston.
Of course, I may also be wrong.
😉
One more "Kudos to Jim!" from my side (and I am sure from John's as well).
Keep well and shoot straight!
HM
Sadly for the "micro-surge" theory, if we return to a previously posted plot of the Cometa's recoil...
...we see no evidence of surge (negative-going g-force in this representation) until piston deceleration begins ~10ms into the discharge sequence and long after WWW has ended.
So whatever's causing the WWW, "micro-surge" isn't it. WWW is a rotational phenomenon -- not a longitudinal one.
And it was that little "surge" at around your mentioned 2.5 ms that I was addressing/trying to hypothesize about. Without a corresponding movement of the action (and therefore a rotation around the CoG or point of hold) there is no cause for movement of the muzzle. ¿IS there?
And it was that little "surge" at around your mentioned 2.5 ms that I was addressing/trying to hypothesize about. Without a corresponding movement of the action (and therefore a rotation around the CoG or point of hold) there is no cause for movement of the muzzle. ¿IS there?
Perhaps I misunderstood you?
HM
Please recall the subject of this thread. Those are plots of Transverse (Vertical Plane) Vibration of the rifle barrel. Not of longitudinal acceleration, of which "surge" is a component, but only late in the recoil sequence when piston deceleration begins.
Meanwhile, the direction of rotation caused by recoil depends on the relationship of CM to piston axis, and since different components (e.g. action vs stock) of the gun have different CMs. they can have different directions of rotation in reaction to the same direction of recoil.
E.g., elevation for the stock, depression for the action.
Thinking about the sequence of events, and noting that what I think you call WWW is more pronounced in the "firm hold" case, PERHAPS we can think of this as being just the moment when the gun goes backwards, but because it is supported at the back by the shoulder/buttpad, the rearward movement induces a muzzle "dip", once contact with the forward hand has reached the compression limit, then the muzzle flips.
No need for the barrel block / detente to flex or partially unlock. It's just the way you would expect a train of objects to buckle down upon first contact to then jump up when the resistance becomes high enough.
Thinking about the sequence of events, and noting that what I think you call WWW is more pronounced in the "firm hold" case,
HM
I think the most fascinating (and mysterious) aspect of the WWW is how it almost disappears completely in the "artillery hold" plot, with a peak amplitude of only ~50um = 0.002" = 0.3MOA.
@steve-in-nc Otherwise, wouldn't the resilience of wood and carpet allow at least some rotation around the CM?
It might not have been the same cradle, but the same basic design and material. The wood upright grain runs vertically, so good compression resistance, but there will be a little give in the short pile carpet.
An accelerometer attached at the muzzle of my HW95. I don't know which accelerometer it was, so can't give a volt per G figure.
Relative to the rifle (which is upside down in the cradle), positive is down, negative up.
I'm sure that was crystal clear to you as you typed it, but it lost something in translation. However, I'm guessing that since the point of your post was to give an example of WWW, the initial positive excursion probably represents muzzle deflection in the direction of trajectory depression rather than the net elevation expected of recoil in an unconstrained gun.
That's such a nicely symmetrical sinusoidal oscillation it's hard to tell if there was any net displacement at all. If you have the original dataset, you might consider doing the double integration on it to see.
Voila! Dyed in the wool Wrong-Way-Wiggle -- but only in the unweighted case. And I take it that here polarity has been reversed from the acceleration plot, so that positive = elevation. Correct?
Thinking about the sequence of events, and noting that what I think you call WWW is more pronounced in the "firm hold" case,
HM
I think the most fascinating (and mysterious) aspect of the WWW is how it almost disappears completely in the "artillery hold" plot, with a peak amplitude of only ~50um = 0.002" = 0.3MOA.
Steve, I know and do keep in mind the differences between muzzle flips/dips and linear displacements of the gun along its "main axis" recoil/surge. One aspect is that the displacement along the main axis is the "motor" of all other movements. If we want to find the SOURCE of the WWW's (as you call them) we need to look into WHERE they get the energy from. The other possibility is that what is, at the moment of firing a "free" system, becomes a restricted one immediately afterwards due to the addition of resisting forces.
My first post was along the first idea, my second post was about something changing at the moment of the start of the recoil. BOTH are plausible:
A firm hold will, usually, imply SOME sort of shoulder contact. Therefore the initial recoil forces the muzzle DOWN (muzzle dip) as the heel of the buttpad is the first point of contact and can only start moving the muzzle up when the rest of the buttpad makes contact, the forward had makes full contact with the forearm, and the inertial forces make the rifle rotate around the CoG and, then, the muzzle flips.
A good and easy way to experiment this is by placing only the toe of the buttpad against the shoulder and running a test, and see what the WWW's do.
Now, in all honesty, I don't think that would divert my attention from the fact that the POSITION of the muzzle is most stable over the immediate vicinity of time of the pellet exit in the "firm hold" case than in the "artillery hold" case.
In the artillery hold case, the position of the muzzle is changing rapidly at the moment of pellet exit; in the firm hold case, the position of the muzzle is coming out of a changeing state and heading to a steady position that lasts a few tenths of ms. THAT is the region I want my pellets to exit at. And there is no semblance of that at any near-in-time point in the Artillery Hold case.
Of course, all this starts from the predicate that the curves are THAT smooth, which I would tend to suspect a little given the extreme complexity, speed, and violence of the mechanical drivers in these machines.
I like a LOT your idea, just think that, for practical purposes, it needs some more resolving power and less "inteference" with the "finished" gun.
Voila! Dyed in the wool Wrong-Way-Wiggle -- but only in the unweighted case. And I take it that here polarity has been reversed from the acceleration plot, so that positive = elevation. Correct?
OK! SOOOOOOooooo, if the muzzle is heavier, then the muzzle does not dip as much.
If the muzzle is lighter, then it dips more.
Given the architecture of the HW95, with the barrel at the top of the compression chamber's main axis it makes sense ¿no?
If the SAME energy is imparted to a light, and a heavy, muzzle it makes the light muzzle move more.
If you amplify Jim's chart there IS a small section of blue UNDER the zero line. Just very small.
In Jim's case, the blue line shows a region of no change in the critical times (though the pellet exit is not noted).
@jim-in-UK
I don't know what your theory of muzzle mass was, but I do think that, IF this chart is TYPICAL of the shot cycle, and IF the pellet exited in the 9 to 11 ms time frames the "WITH" weight configuration of the gun should have been more accurate than the "MINUS" version.
@hector-j-medina-g It was more accurate from the bench with the added mass at the muzzle, Hector.
That said, away from the bench in three positional (prone, kneeling and standing) HFT, any extra mass at the muzzle seems good.
Not to belabor the obvious, but although the focus of this thread is ballistical (sic?), there are certainly other factors in play in the achievement of accurate shooting and weight distribution might affect many of them. For example, first the gun must be accurately aimed and held on the POA before the firing sequence even begins.
@hector-j-medina-g It was more accurate from the bench with the added mass at the muzzle, Hector.
That said, away from the bench in three positional (prone, kneeling and standing) HFT, any extra mass at the muzzle seems good.
Not to belabor the obvious, but although the focus of this thread is ballistical (sic?), there are certainly other factors in play in the achievement of accurate shooting and weight distribution might affect many of them. For example, first the gun must be accurately aimed and held on the POA before the firing sequence even begins.
I made the point because, from the bench, I found that increasing mass muzzle might reduce group size, but there comes a point at which that reverses, presumably because pellet exit coincided with an antinode, but then moved away with further mass increase.
In 'field' shooting, the benefits of going above the 'sweet' mass seem to outweigh any tiny loss of accuracy due to muzzle vibration and pellet exit timing.
I made the point because, from the bench, I found that increasing mass muzzle might reduce group size, but there comes a point at which that reverses, presumably because pellet exit coincided with an antinode, but then moved away with further mass increase.
In 'field' shooting, the benefits of going above the 'sweet' mass seem to outweigh any tiny loss of accuracy due to muzzle vibration and pellet exit timing.
Interesting. Jim!
MOST (about 80%) of all my shooting is done from the knee, 10% from kneeling, and 10% from standing.
Even the testing of "finished guns" gets done this way because I want to assess not only the precision/accuracy of the airgun itself, but how "shootable" it is.
A gun may be the MOST ACCURATE and PRECISE gun in the world. If it's not "shootable" it is not "interesting" (to very specifically go against one of the Great American Gunwriters -Townsend Whelen-) LOL!.
In the same way that adding mass to a muzzle changes the vibrations, lengthening or shortening the distance between beginning of barrel and end (not necessarily the muzzle/crown), also affects and yes, there is a "periodicity" to this.
If you look at this picture:
You can see that. The other thing I have found, that seems to hold almost universally, is that as you lengthen the distance to the "tuning mass" the main axis of the group goes from vertical to horizontal and viceversa, which to me means that the muzzle oscillates in all directions. I usually settle for the best and roundest position.
I am not so sure that level of power involved in the compression/distension of the internals of the barrel in an airgun are enough to affect seriously the actual angle of the last inch/couple of inches of the muzzle as relates to the rest of the barrel, but perhaps with the spaghetti barrels so much in vogue today at the high energies (approaching a 0.22" RF), this could also be a factor.
That's something I have learned today! When Mike Wright and I experimented with a tuning mass (24% that of the barrel) we were not looking for group orientation, only ctc measurement.
I learned about bench Vs field accuracy a very long time ago, when the HW77 proved not to be the most accurate springer from the bench, but trounced everything else in early FT.
