GTA
All Springer/NP/PCP Air Gun Discussion General => European/Asian Air Gun Gates => German AirGun Gate => Topic started by: Mark 611 on March 28, 2023, 04:47:33 AM
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Does a pellet exit the barrel, before the piston hits home? or is the pellet still in the barrel when the piston hits home? for example, my HW's no longer have factory length barrels, let's compare a factory 16'' to a 12.2'' or a 10.5'' barrel length, starting with a 16'' barrel, has the pellet exited before or after the piston hits home ;D
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I have recorded hundreds of recoil cycles (velocity and acceleration, as well as pellet exit), and the pellet exit has in every case been shortly after the completion of the compression stroke, during piston bounce.
Available evidence suggests the pellet is in the region of 4" up the barrel at the end of the compression stroke.
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I have recorded hundreds of recoil cycles (velocity and acceleration, as well as pellet exit), and the pellet exit has in every case been shortly after the completion of the compression stroke, during piston bounce.
Available evidence suggests the pellet is in the region of 4" up the barrel at the end of the compression stroke.
Hello Jim in UK,
Was this with a 12 FPE .177 break barrel?
Thanks.
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Hello Jim in UK,
Was this with a 12 FPE .177 break barrel?
Thanks.
Hi. Because I'm in the UK, all my experiments are of necessity sub 12 ft. lb., and mainly .177".
There is research more pertinent to higher muzzle energy on page #11 of this thread.
https://www.gatewaytoairguns.org/GTA/index.php?topic=176445.0 (https://www.gatewaytoairguns.org/GTA/index.php?topic=176445.0)
The 4" is just a ball park figure, and will vary according to pellet start pressure, calibre, and available piston stroke.
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Mark,
As Hector once explained to me, the most accurate guns are when the pellets is leaving the barrel at the same time that the piston comes to its initial stop from the forward motion.
Supposedly, this keeps the harmonic vibrations of the barrel to a minimum until the pellet is out of the barrel. He called it "pellet dwell time".
-Y
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Thanks' YOGI, JIM in the UK, I have several different power levels, MY R1's are at full power, {FAC} 1 in .20cal and the other is a .22cal both have 12.2'' barrels, my HW50's 1 in .20cal has an 11'' barrel @10'5ftlbs, my .22cal HW50 also has a 10.5'' barrel @11.9ftlbs these are the general power ranges my guns are tuned at 8)
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Deleted.
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Mark,
As Hector once explained to me, the most accurate guns are when the pellets is leaving the barrel at the same time that the piston comes to its initial stop from the forward motion.
Supposedly, this keeps the harmonic vibrations of the barrel to a minimum until the pellet is out of the barrel. He called it "pellet dwell time".
-Y
I have to admit that does sound pretty interesting to me.
Imagine a gun with heavy (for a springer) rearward recoil yet no forward recoil and very very accurate due to the stiff short barrel. This at the price of reduced velocity.
A few problems that need to be overcome:
1. Cocking force needed would likely be high even with a side lever. Maybe a hand crank for compressing the spring is the best way of achieving this?
2. Timing the projectile exit with piston deceleration such that the piston comes to a soft landing on the breech without first bouncing back (which also generates a forward recoil). Remember that once the projectile leaves the barrel there will be a sudden pressure drop in the compression chamber thus the piston needs to be almost completely decelerated before this happens.
3. Since this type of springer will only operate with a very very narrow range of projectiles the ideal projectile must be selected ahead of time. The gun thus would be built around the projectile. If the choice were up to me the projectile the gun would be built around would be one of the 2nd generation BBTs (which have boat tail optimization suggestions from Miles Morris incorporated into them) found here:
https://www.gatewaytoairguns.org/GTA/index.php?topic=206009.0 (https://www.gatewaytoairguns.org/GTA/index.php?topic=206009.0)
Note: Bob's Boat tail slugs have reduced diameter center sections so even though they are relatively long and properly supported front and rear they will have very low friction in the barrel. Bob also did confirm (when I asked him) that they can also be made in the same swaging machines that make swaged diabolo pellets.
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I'm not having any issues with anything, this subject was brought up elsewhere and just thought I'd try to touch on the subject, my guns are not any harder to cock than with a full-length barrel, unless I put a monster spring in the power plant, the shot barrels I run are pretty common lengths in the U.K. HW's true K models have a 12.2'' barrel length, even with the HW80, I have also not had any velocity loss with the short barrels and accuracy is outstanding, 8)
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I've also read the peak pressure is reached before the pellet exits the barrel. Some guns have short barrels from the factory.
Mendozas like my RM2800 have a barrel about 17 inches long but only the first 12 inches is rifled and it's bored out a little larger to the end.
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I've also read the peak pressure is reached before the pellet exits the barrel. Some guns have short barrels from the factory.
Mendozas like my RM2800 have a barrel about 17 inches long but only the first 12 inches is rifled and it's bored out a little larger to the end.
Yes, peak pressure is much earlier. However, as the pellet moves down the barrel is drops.
In larger calibers it drops much faster than .177 does.
-Y
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I'm not having any issues with anything, this subject was brought up elsewhere and just thought I'd try to touch on the subject, my guns are not any harder to cock than with a full-length barrel, unless I put a monster spring in the power plant, the shot barrels I run are pretty common lengths in the U.K. HW's true K models have a 12.2'' barrel length, even with the HW80, I have also not had any velocity loss with the short barrels and accuracy is outstanding, 8)
Oh yeah, I wasn't thinking of your guns. I was actually trying to imagine how a hypothetical experimental gun greater than 12 fpe would operate. This because in post #2 of this thread it was mentioned the pellet is about 4" down the barrel in a 12 fpe gun when the piston comes to a stop in the compression stroke (i.e.before first bounce on the cushion of air) yet I remember reading in Cardew's book "from trigger to target" the Max velocity for a 12 fpe gun requiring longer than 4" of barrel. A airgun of greater than 12 fpe would necessitate an even longer minimum barrel length than Cardew used. That is the only reason I brought up hand crank or side lever (like Diana 48) rather than guns like 460 magnum or 350 magnum. Obviously if barrel is shortened on 460 magnum it will look awkward as the cocking handle extends past the barrel....and with the 350 magnum if the barrel is shortened it will obviously affect the effort of cocking.
So it seems from my standpoint, at least for Diana guns, the 48 and 54 Air king (which AFAIK is a 48 that uses a sliding sled to reduce recoil) represent the ultimate action from which to build the highest possible accuracy springer. Of course, other companies make side levers but I think the only side lever to be magnum is Diana. I'll check Hatsan though but I don't think they do.
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Does a pellet exit the barrel, before the piston hits home? or is the pellet still in the barrel when the piston hits home? for example, my HW's no longer have factory length barrels, let's compare a factory 16'' to a 12.2'' or a 10.5'' barrel length, starting with a 16'' barrel, has the pellet exited before or after the piston hits home ;D
Hey Yoda,
I thought everyone in the airgun community understood why shooting Springers was a challenge ???
-> The pellet doesn't leave the barrel until piston movement is finished. That's why consistency is so difficult - and why we can't get enough of them ;).
Shorter barrels should help with this issue .............
If not, PCP's wouldn't be such the rave 8). You don't need much practice with a PCP to get reasonably good accuracy at 30 yards.
Good to hear from you Mark :D
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Thank, Kirk ;D, I don't get here much anymore, I've been spending a lot of time with the big bang sticks! and lots of range time, I spend a lot of time on other forums these days :o
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I have recorded hundreds of recoil cycles (velocity and acceleration, as well as pellet exit), and the pellet exit has in every case been shortly after the completion of the compression stroke, during piston bounce.
Available evidence suggests the pellet is in the region of 4" up the barrel at the end of the compression stroke.
Curiosity has gotten the best of me. How do you determine all of this. It would seem to me that a lot of expensive, precision equipment to measure piston position relative to pellet postition in the barrel, and how does one determine at a specific time the position of a pellet in a barrel.
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I have recorded hundreds of recoil cycles (velocity and acceleration, as well as pellet exit), and the pellet exit has in every case been shortly after the completion of the compression stroke, during piston bounce.
Available evidence suggests the pellet is in the region of 4" up the barrel at the end of the compression stroke.
Curiosity has gotten the best of me. How do you determine all of this. It would seem to me that a lot of expensive, precision equipment to measure piston position relative to pellet postition in the barrel, and how does one determine at a specific time the position of a pellet in a barrel.
I think all the experts and A/G makers and designers figure this stuff out and we read about it.
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I would agree with that, this why the shortest barrels on HW break barrels are at 12.2'' the 97k is 11'' MY COMETA 400 compact is around 11'' I think? these barrel lengths still produce the same velocities as the longer barrels, look at the TX200 barrel length 9.5'' HC models are like 8.5'' ;)
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Curiosity has gotten the best of me. How do you determine all of this. It would seem to me that a lot of expensive, precision equipment to measure piston position relative to pellet postition in the barrel, and how does one determine at a specific time the position of a pellet in a barrel.
Fair questions, Jeff, and not easily answered.
I would love to directly measure piston position in the cylinder during the compression stroke, peak cylinder temperature and pressure, as well as pellet position in the barrel, but there is no way I could afford the necessary equipment, so I have to get inventive and measure what I can.
I measure recoil relative velocity (with a coil and magnet) and actual acceleration (from which I can find peak cylinder pressure), and I can record pellet exit and muzzle velocity. I previously measured the start pressures for a range of .177" pellets, and have conducted experiments to find piston maximum travel. Putting this all together...
Integrating the relative recoil velocity data gives relative recoil displacement, which I can scale by plugging in actual measured displacement, or from which I can get a pretty accurate graph of piston position by plugging in the maximum travel from aforementioned previous experiments. I can add the pellet start and exit points to the piston travel graph to find the pellet barrel transit time. I now rely on test data from John Bowkett and the late David Robson on pellet acceleration to estimate pellet position at piston bounce, which is corroborated by test data from GTA members on the thread I linked to earlier, as well as the peak cylinder pressures I record (by looking at combinations of peak piston travel and pellet position that would generate the recorded peak pressure).
I hope this makes sense.
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Empirical data seems consistent with theoretical predictions here
https://www.researchgate.net/publication/274638905_Internal_Ballistics_of_Spring_Piston_Airguns (https://www.researchgate.net/publication/274638905_Internal_Ballistics_of_Spring_Piston_Airguns)
Basically the pellet "starts" to move as piston nears the END of its forward travel and does not exit the muzzle until after the piston has either stopped or is rebounding a short distance. The shooter "feels" the rearward recoil of piston launch AND the forward recoil of piston stop/rebound before the pellet exits the muzzle. Those recoils coupled with barrel vibrations that are in progress WHEN the pellet exits the muzzle are why springers are difficult to shoot accurately.
There was an EXCELLENT high speed video of a springer "dancing" as the pellet exited the muzzle. In slow motion it really looks like the springer is shaking itself apart, yet springers do that "dance' every shot for many thousands of shots. No surprise that springers can kill scopes. I'll post the link if I can find it again.
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Interesting reading here.
At first I wanted to measure the barrel lengths on my Springers to see if the more accurate ones had longer or shorter barrels. HW-98, R-10, and R-9, FWB 124....
But then it dawned on me that the compression tube length plays into the piston travel distance. So that would determine when the recoil changes direction and the amount it travels in conjunction with the barrel length.
Way too much math this early in the morning. ::)
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Scott, your reading my mind! :P
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Interesting reading here.
At first I wanted to measure the barrel lengths on my Springers to see if the more accurate ones had longer or shorter barrels. HW-98, R-10, and R-9, FWB 124....
But then it dawned on me that the compression tube length plays into the piston travel distance. So that would determine when the recoil changes direction and the amount it travels in conjunction with the barrel length.
Way too much math this early in the morning. ::)
Scott,
You forgot the size and shape, and location, of the transfer port as well..... ::)
-Y
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Interesting reading here.
At first I wanted to measure the barrel lengths on my Springers to see if the more accurate ones had longer or shorter barrels. HW-98, R-10, and R-9, FWB 124....
But then it dawned on me that the compression tube length plays into the piston travel distance. So that would determine when the recoil changes direction and the amount it travels in conjunction with the barrel length.
Way too much math this early in the morning. ::)
Scott,
You forgot the size and shape, and location, of the transfer port as well..... ::)
-Y
Not only that but the strength of the spring (plus whether it is a linear rate spring or a progressive rate spring), piston weight, friction of projectile within barrel, projectile caliber and weight, barrel length.... just to make a few.
Of particular interest is the strength of the spring compared to the piston weight. Logic follows kinetic energy of the piston during compression will increase with increasing piston weight up until a point and then further increasing piston weight results in decreasing kinetic energy. If we are trying to get rid of forward recoil (from piston bounce) by having the projectile leave the barrel right at the point where the piston has reached near zero velocity then matching piston weight to spring strength is critical. This along with having a low friction between barrel and projectile.
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It seems to me, (I could be completely wrong on this) that if the pellet has not exited the barrel before the piston rebounds that there would be a brief "sucking effect" on the pellet which might have a destabilizing effect from shot-to-shot depending on the pellet's ability to seal in the bore consistently.
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It seems to me, (I could be completely wrong on this) that if the pellet has not exited the barrel before the piston rebounds that there would be a brief "sucking effect" on the pellet which might have a destabilizing effect from shot-to-shot depending on the pellet's ability to seal in the bore consistently.
I am by no means competent to really answer this, my background in medical science. but I would think the distance the piston would have to rebound to create your sucking effect would have to be a distance so the volume of the cylinder creating the sucking effect would have to be greater than the volume in the barrel behind the pellet. I would think it would certainly decrease the pressure behind the pellet, but is that enough to overcome the inertia of the moving pellet. This whole concept sounds like a bucket of worms to me.
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It seems to me, (I could be completely wrong on this) that if the pellet has not exited the barrel before the piston rebounds that there would be a brief "sucking effect" on the pellet which might have a destabilizing effect from shot-to-shot depending on the pellet's ability to seal in the bore consistently.
I am by no means competent to really answer this, my background in medical science. but I would think the distance the piston would have to rebound to create your sucking effect would have to be a distance so the volume of the cylinder creating the sucking effect would have to be greater than the volume in the barrel behind the pellet. I would think it would certainly decrease the pressure behind the pellet, but is that enough to overcome the inertia of the moving pellet. This whole concept sounds like a bucket of worms to me.
The pellet is typically too far down the barrel when the piston bounces for the change in pressure to have a material impact. There are remedies that custom tuners have devised to reduce piston bounce. I’ve heard that Hector for example has a dead blow hammer design that drives the piston forward just when it’s about to bounce. Personally, I think a more desirable approach is to tune the spring, piston and transfer port to ensure that the piston comes to “gentle” stop at the end of the compression chamber. That said, it’s not an easy thing to do without extensive testing while varying preload, piston mass and TP diameter.
-Marty
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It seems to me, (I could be completely wrong on this) that if the pellet has not exited the barrel before the piston rebounds that there would be a brief "sucking effect" on the pellet which might have a destabilizing effect from shot-to-shot depending on the pellet's ability to seal in the bore consistently.
I am by no means competent to really answer this, my background in medical science. but I would think the distance the piston would have to rebound to create your sucking effect would have to be a distance so the volume of the cylinder creating the sucking effect would have to be greater than the volume in the barrel behind the pellet. I would think it would certainly decrease the pressure behind the pellet, but is that enough to overcome the inertia of the moving pellet. This whole concept sounds like a bucket of worms to me.
The pellet is typically too far down the barrel when the piston bounces for the change in pressure to have a material impact. There are remedies that custom tuners have devised to reduce piston bounce. I’ve heard that Hector for example has a dead blow hammer design that drives the piston forward just when it’s about to bounce. Personally, I think a more desirable approach is to tune the spring, piston and transfer port to ensure that the piston comes to “gentle” stop at the end of the compression chamber. That said, it’s not an easy thing to do without extensive testing while varying preload, piston mass and TP diameter.
-Marty
You think?
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It seems to me, (I could be completely wrong on this) that if the pellet has not exited the barrel before the piston rebounds that there would be a brief "sucking effect" on the pellet which might have a destabilizing effect from shot-to-shot depending on the pellet's ability to seal in the bore consistently.
I am by no means competent to really answer this, my background in medical science. but I would think the distance the piston would have to rebound to create your sucking effect would have to be a distance so the volume of the cylinder creating the sucking effect would have to be greater than the volume in the barrel behind the pellet. I would think it would certainly decrease the pressure behind the pellet, but is that enough to overcome the inertia of the moving pellet. This whole concept sounds like a bucket of worms to me.
The pellet is typically too far down the barrel when the piston bounces for the change in pressure to have a material impact. There are remedies that custom tuners have devised to reduce piston bounce. I’ve heard that Hector for example has a dead blow hammer design that drives the piston forward just when it’s about to bounce. Personally, I think a more desirable approach is to tune the spring, piston and transfer port to ensure that the piston comes to “gentle” stop at the end of the compression chamber. That said, it’s not an easy thing to do without extensive testing while varying preload, piston mass and TP diameter.
-Marty
You think?
I do! It’s the holy grail of tuning 😜
-Marty
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It seems to me, (I could be completely wrong on this) that if the pellet has not exited the barrel before the piston rebounds that there would be a brief "sucking effect" on the pellet which might have a destabilizing effect from shot-to-shot depending on the pellet's ability to seal in the bore consistently.
I am by no means competent to really answer this, my background in medical science. but I would think the distance the piston would have to rebound to create your sucking effect would have to be a distance so the volume of the cylinder creating the sucking effect would have to be greater than the volume in the barrel behind the pellet. I would think it would certainly decrease the pressure behind the pellet, but is that enough to overcome the inertia of the moving pellet. This whole concept sounds like a bucket of worms to me.
The pellet is typically too far down the barrel when the piston bounces for the change in pressure to have a material impact. There are remedies that custom tuners have devised to reduce piston bounce. I’ve heard that Hector for example has a dead blow hammer design that drives the piston forward just when it’s about to bounce. Personally, I think a more desirable approach is to tune the spring, piston and transfer port to ensure that the piston comes to “gentle” stop at the end of the compression chamber. That said, it’s not an easy thing to do without extensive testing while varying preload, piston mass and TP diameter.
-Marty
You think?
I do! It’s the holy grail of tuning 😜
-Marty
Absolutely, balancing all those factors is what it is all about. Tophat, spring guide, spring, is just the beginning. ;)
-Y
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I dragged out both of my Cometa 220 compacts in.177cal today both of them have barrels way shorter than the power plant, they are tune and sound like a PCP when fired, 1 still has the can on it the other I removed, both are factory barrel lengths ;D
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Sometimes I am just happy if the pellet leaves the barrel.... ;D ;D ;D
-Y
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It seems to me, (I could be completely wrong on this) that if the pellet has not exited the barrel before the piston rebounds that there would be a brief "sucking effect" on the pellet which might have a destabilizing effect from shot-to-shot depending on the pellet's ability to seal in the bore consistently.
I am by no means competent to really answer this, my background in medical science. but I would think the distance the piston would have to rebound to create your sucking effect would have to be a distance so the volume of the cylinder creating the sucking effect would have to be greater than the volume in the barrel behind the pellet. I would think it would certainly decrease the pressure behind the pellet, but is that enough to overcome the inertia of the moving pellet. This whole concept sounds like a bucket of worms to me.
The pellet is typically too far down the barrel when the piston bounces for the change in pressure to have a material impact. There are remedies that custom tuners have devised to reduce piston bounce. I’ve heard that Hector for example has a dead blow hammer design that drives the piston forward just when it’s about to bounce. Personally, I think a more desirable approach is to tune the spring, piston and transfer port to ensure that the piston comes to “gentle” stop at the end of the compression chamber. That said, it’s not an easy thing to do without extensive testing while varying preload, piston mass and TP diameter.
-Marty
You think?
I do! It’s the holy grail of tuning 😜
-Marty
Absolutely, balancing all those factors is what it is all about. Tophat, spring guide, spring, is just the beginning. ;)
-Y
Can you name any examples of where this has occurred? (A rifle that has a piston which doesn't rebound (i.e. bounce off the cushion of air in the compression chamber) and instead makes a gentle stop at the end of the compression stroke before the projectile leaves the barrel.)
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Pressure behind pellet is always positive during the shot cycle. It does drop and rise during piston bounce...because the pressure acting on the largely different areas causes the bounce! NEVER is pressure negative or trying to "vacuum" the pellet.
Piston bounce happens more often than most think. It is also NOT as big problem as most think. The 2 recoils occur before the pellet leaves the muzzle. Even during the ideal and rare "piston soft landing" condition, the 2nd recoil IS the piston landing! ... and the pellet is still in the bore.
SOME pellet energy is lost because of piston bounce but it is a SMALL percentage.
What the "soft landing" should provide is the MINIMUM 2nd recoil and the THEORETICAL best energy transfer to the pellet. If those marginal benefits can be obtained using SIMPLE COST EFFECTIVE tuning techniques then I'm in. Smoothest shot cycle, best accuracy, and then best pellet energy is what I aim for on every springer I own/tune.
However, if trying to gain ~1% more energy or ~1% less 2nd recoil I need to " redesign (https://en.wikipedia.org/wiki/Rube_Goldberg_machine)" a simple springer into some overly complex expensive failure prone mechanical nightmare then I'm out. So are most springer makers.
IMO springer manufacturers have known about springer physics for MANY years through empirical testing and more recently through detailed computational analysis and finite element simulation. Why "we" think we know MORE than they do without those deep resources is puzzling to me.
I'll sit back and lurk while the overthink wheels spin... eventually burn out.. and restart again in the near future. I smell overheating rubber already ;-)
For those NEW to springers, no offense intended. It is a deceptively simple system with a very complex behavior.
Folks with more springer experience should understand my comments.
For those who just like to dream of perfection, please keep dreaming (and reading and learning). Eventually one of those dreams may help make springers marginally better.
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Pressure behind pellet is always positive during the shot cycle. It does drop and rise during piston bounce...because the pressure acting on the largely different areas causes the bounce! NEVER is pressure negative or trying to "vacuum" the pellet.
Piston bounce happens more often than most think. It is also NOT as big problem as most think. The 2 recoils occur before the pellet leaves the muzzle. Even during the ideal and rare "piston soft landing" condition, the 2nd recoil IS the piston landing! ... and the pellet is still in the bore.
SOME pellet energy is lost because of piston bounce but it is a SMALL percentage.
What the "soft landing" should provide is the MINIMUM 2nd recoil and the THEORETICAL best energy transfer to the pellet. If those marginal benefits can be obtained using SIMPLE COST EFFECTIVE tuning techniques then I'm in. Smoothest shot cycle, best accuracy, and then best pellet energy is what I aim for on every springer I own/tune.
However, if trying to gain ~1% more energy or ~1% less 2nd recoil I need to " redesign (https://en.wikipedia.org/wiki/Rube_Goldberg_machine)" a simple springer into some overly complex expensive failure prone mechanical nightmare then I'm out. So are most springer makers.
IMO springer manufacturers have known about springer physics for MANY years through empirical testing and more recently through detailed computational analysis and finite element simulation. Why "we" think we know MORE than they do without those deep resources is puzzling to me.
I'll sit back and lurk while the overthink wheels spin... eventually burn out.. and restart again in the near future. I smell overheating rubber already ;-)
For those NEW to springers, no offense intended. It is a deceptively simple system with a very complex behavior.
Folks with more springer experience should understand my comments.
For those who just like to dream of perfection, please keep dreaming (and reading and learning). Eventually one of those dreams may help make springers marginally better.
Does this piston soft landing condition involve piston bounce? Or is it merely involve a piston pause (without a bounce) then the soft landing occurs?
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NT
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Does this piston soft landing condition involve piston bounce? Or is it merely involve a piston pause (without a bounce) then the soft landing occurs?
There is no piston bounce in the "ideal soft landing case", but the second recoil is still present and the pellet still does not leave the barrel before the second recoil occurs. Basically the second recoil is the air being compressed and pushing back on the piston face. This is how a springer works. No second recoil=no air compression=no force to move pellet. You can minimize the second recoil by minimizing piston bounce but you can never eliminate the second recoil.
https://www.gatewaytoairguns.org/GTA/index.php?topic=207217.msg156435167#msg156435167 (https://www.gatewaytoairguns.org/GTA/index.php?topic=207217.msg156435167#msg156435167)
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I bet that Hollywood stunt man hopes the pellet don't leave his air bag too soon when he falls off the 20 story building. :o
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I guess in my case on my rifles, I do not even notice the second bounce from the pistons, but I have had some rifles where it was definitely noticeable, been a lot of interesting information posted, thanks guys! 8)
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What we "feel" when shooting a springer is a firm nudge (force) into the shoulder as the piston is accelerated forward from rest. After about 8/1000 of a second the piston is coming to a very short stop on a high pressure slug of air lasting only about 1/1000 of a second. That abrupt deceleration can be felt as a forward surge force but can also be perceived as an abrupt HALT to the recoil force. Regardless of how it is perceived BOTH forces MUST OCCUR. It is the simple physics of force action/reaction in motion systems.
Because both forces are short duration and close together in "our" perceived time frame, shooting a well tuned springer will usually feel like a single* solid THUMP! It is important to note that the pellet is still traveling down the barrel when we feel this THUMP. About 1/1000 of a second AFTER the THUMP the pellet actually leaves the barrel.
In many cases the piston decelerates to a stop and reverses direction for a short distance. Theoretically this piston reversal can be eliminated to gain a little more pellet energy. That tuning effort is LARGE for a SMALL gain and will only work for a very narrow set of conditions. Change ANY of those conditions and a piston bounce will re-occur. It is NOT WORTH THE EFFORT to completely eliminate the "first" piston bounce.
AFTER the pellet leaves the barrel the piston returns from its short backwards trip onto an empty breech. This no-backpressure "collision" is not as large as the deceleration event because most of the system energy is already dissipated. But the collision does vibrate the rifle and send shockwaves through the coil spring which can cause another smaller piston bounce. In total there can be several collisions/bounces after the shot with EACH smaller collision sending shockwaves up/down the coil spring length. THIS is what we perceive as a buzzy-twangy springer. The LATE piston bounces do NOT affect accuracy since the pellet has already exited the muzzle. The late bounces & buzzes DO affect spring life and can make the shooting experience unpleasant.
With MINIMAL effort, such as installing a properly fitted spring guide, the "late" bounces/collisions AND the associated coil spring shocks/vibrations can be reduced. IMO springer tuning to reduce these IS WORTH THE EFFORT!
-------------------- "Hacking The Benjamin Titan NP Break Barrel" thread ...
https://www.gatewaytoairguns.org/GTA/index.php?topic=176445.msg155995664#msg155995664 (https://www.gatewaytoairguns.org/GTA/index.php?topic=176445.msg155995664#msg155995664)
https://www.gatewaytoairguns.org/GTA/index.php?topic=176445.msg156102451#msg156102451 (https://www.gatewaytoairguns.org/GTA/index.php?topic=176445.msg156102451#msg156102451)
https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=176445.0;attach=348837;image (https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=176445.0;attach=348837;image)
-------------------------- Travella's Published Papers...
https://www.researchgate.net/publication/274638905_Internal_Ballistics_of_Spring_Piston_Airguns (https://www.researchgate.net/publication/274638905_Internal_Ballistics_of_Spring_Piston_Airguns)
https://www.researchgate.net/publication/277953420_Spring_Buzz_and_Failure_in_Spring_Piston_Airguns (https://www.researchgate.net/publication/277953420_Spring_Buzz_and_Failure_in_Spring_Piston_Airguns)
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Barrel length does play some part in all this. Depending on the swept volume and bore size the pellets in longer barrels (say 16"?) are usually STILL accelerating but MOST of the acceleration happens within the first 10" of barrel length. Does that mean we should ALL cut our springer barrels down to 10" or less? I SAY NO!
Muzzle weights and barrel crops MAY improve a springers performance by changing barrel vibrations/harmonics. Changing the position and mass of a muzzle weight is non-destructive and reversible. There is no easy reversible way I know of to determine if a particular springer would benefit from a barrel length crop. It would be trial & error for each and every rifle. Crop an inch, recrown, test & record data for dozens of different pellets, then repeat. You will only find a sweet spot (if it exists) by cutting one time too short!
NONE of my springers is shooting bad enough to risk incremental barrel crops and expend the effort needed to document all the results. I'm happy to leave that effort for someone else.
edit: I found the slowmo video of a springer doing its dance. It was related to AOA testing the Diana ZR mount. You can watch the entire video normal speed but I suggest watching from the time linked at 0.25 speed. https://youtu.be/bBLiIeoxGTg?t=73 (https://youtu.be/bBLiIeoxGTg?t=73)
Presenter sounds WASTED if you listen to him talking at 0.25 speed. Good video overall ;-)
*A few years ago, before I really understood how springers work, I wanted to shoot a sub 10 fpe springer in my basement. I detuned an old B19 style springer by eliminating all of the spring preload. Normal spring preload in the rifle was about 2". That put it close to 6 fpe. It worked, barely, but the rifle had THE LONGEST shot cycle I've ever experienced. Trigger click, pause, THUMP, pause, pellet exit, pellet hits target, pause, ssshhh-thump#2 as the piston finally returned home from its one and only bounce! A really weak double-thumping springer. That's an extreme case but it is also the first time I realized piston bounce was a real thing. The B19 went back to full power and I found a perfect fit 5fpe youth springer for that project.
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I found the slowmo video of a springer doing its dance. It was related to AOA testing the Diana ZR mount. You can watch the entire video normal speed but I suggest watching from the time linked at 0.25 speed. https://youtu.be/bBLiIeoxGTg?t=73 (https://youtu.be/bBLiIeoxGTg?t=73)
Michael;
That video is flawed in many ways.
If you look closely to the times annotated in the video, you will note that the gun starts to move back at ms -408.8
Then the maximum excursion OF THE MOUNT is achieved at ms -398.1
Then the MOUNT bounces at ms 393.5 and then bounces again later at an undisclosed time.
Compare that shot cycle with the one in this video:
https://youtu.be/xA8aELcv_fY
And you will see that the gun actually completes the shot cycle before the ZR mount can catch up with it.
;-)
Keep well and shoot straight!
HM
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I found the slowmo video of a springer doing its dance. It was related to AOA testing the Diana ZR mount. You can watch the entire video normal speed but I suggest watching from the time linked at 0.25 speed. https://youtu.be/bBLiIeoxGTg?t=73 (https://youtu.be/bBLiIeoxGTg?t=73)
Michael;
That video is flawed in many ways.
If you look closely to the times annotated in the video, you will note that the gun starts to move back at ms -408.8
Then the maximum excursion OF THE MOUNT is achieved at ms -398.1
Then the MOUNT bounces at ms 393.5 and then bounces again later at an undisclosed time.
Compare that shot cycle with the one in this video:
https://youtu.be/xA8aELcv_fY
And you will see that the gun actually completes the shot cycle before the ZR mount can catch up with it.
;-)
Keep well and shoot straight!
HM
Sorry Hector, I don't understand the point you are trying make.
I referenced the video to show how much a springer jumps and dances before the pellet leaves the barrel. The clear and time-stamped AOA video at 10000 frames per second looks spot-on to me. Shot cycle duration approximately 10ms (-408ms to -398ms) with pellet likely leaving the muzzle around -396ms(?). What is interesting to me in the AOA video is the all the additional movements (dancing & flexing) of the action, the end cap, and the safety lever that highlight how violent a springer shot cycle really is.
The Diana ZR mount in the AOA video looks to me like it is doing its job exceptionally WELL!. Scope appears to be almost completely isolated from the LARGE springer movements. Yes the scope is slowly moving/recovering its "zero" position after the initial shot/rifle-dance. The scope may even bounce a little in the mount but that is what I would expect to see from a slightly underdamped vibration/shock isolation system.
Anyone watching the AOA video should see confirming evidence of at least three things we "thought we knew" about springers and scopes.
1) Springers jump and vibrate A LOT during/after a shot.
2) A ~10ms shot cycle time calculated/simulated/measured for major piston/rifle movements is very close.
3) A Diana ZR mount can isolate a scope VERY WELL from the most violent springer motions.
I see essentially the same thing in the low res video clip. The rifle jumps while the scope slowly reacts and lags behind the rifle movements as the ZR mount does its isolation thing.
Are you suggesting that the ZR mount in the AOA video is too underdamped and needs to be better adjusted or "tuned"?
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Sorry Hector, I don't understand the point you are trying make.
I referenced the video to show how much a springer jumps and dances before the pellet leaves the barrel. The clear and time-stamped AOA video at 10000 frames per second looks spot-on to me. Shot cycle duration approximately 10ms (-408ms to -398ms) with pellet likely leaving the muzzle around -396ms(?). What is interesting to me in the AOA video is the all the additional movements (dancing & flexing) of the action, the end cap, and the safety lever that highlight how violent a springer shot cycle really is.
The Diana ZR mount in the AOA video looks to me like it is doing its job exceptionally WELL!. Scope appears to be almost completely isolated from the LARGE springer movements. Yes the scope is slowly moving/recovering its "zero" position after the initial shot/rifle-dance. The scope may even bounce a little in the mount but that is what I would expect to see from a slightly underdamped vibration/shock isolation system.
Anyone watching the AOA video should see confirming evidence of at least three things we "thought we knew" about springers and scopes.
1) Springers jump and vibrate A LOT during/after a shot.
2) A ~10ms shot cycle time calculated/simulated/measured for major piston/rifle movements is very close.
3) A Diana ZR mount can isolate a scope VERY WELL from the most violent springer motions.
I see essentially the same thing in the low res video clip. The rifle jumps while the scope slowly reacts and lags behind the rifle movements as the ZR mount does its isolation thing.
Are you suggesting that the ZR mount in the AOA video is too underdamped and needs to be better adjusted or "tuned"?
Michael;
Sorry for not making myself clear.
First off, the video was not commissioned by AoA, it was commissioned by DIANA. It was made with Gen I mounts i a German spec gun.
You are right in that the spring in the mount in the video is OVER reacting, it makes the scope close on the mount before the shot cycle finishes.
And then it separates and closes again.
ZR Mounts do not "dampen" anything, they are supposed to "FLOAT" the scope while the shot cycle is going on. Once the shot cycle is done, THEN the mount should return to battery. For that we need the excursion of the mount to be at least 6-8 mm's to the rear. Which is not the case in the video.
What we discovered in the video you showed as "AoA" was that the mount did not work too well in rifles of less than 13 ft-lbs yield (the rifle in the video had a 7 ft-lbs yield), and that the return spring had to be "weakened" a bit to make the mounts work well in the 12 ft-lbs region.
STILL, the mounts are not recommended for less than 8-9 ft-lbs (exception being those guns with sleds).
For guns with a yield of around 12 ft-lbs and using heavy scopes, I still prefer the higher return force of the Gen I mounts spec.
That spring guns jump and buck like wild bull at a rodeo has been made evident in many other videos, and what we have learned, after some years of ZR mounts in existence and operation is that the MAIN problem for scopes is not the (in)famous "double recoil" but the vibrations transmitted to the erector group/tube during the shot cycle.
Therefore current Gen III or IV ZR mounts DO work exceptionally well because we learned a lot from that video and from the thousands of mounts currently in circulation.
ZR Mounts do work well and, yet, there are always things that can be improved.
The "chase" that's still going on is how to make the pellet exit the barrel ASAP. Before harmonics can flow to the muzzle and before the piston bounce jacks up to 11 the vibrations.
Again, apologies for not making myself clear.
Keep well and shoot straight!
HM
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Thank you Hector for the detailed explanation!
I suspected the mounts might need some rifle specific tuning and your response will be very helpful when I finally install the ZR mount I have still new in box.
Cheers :-)