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[Sticky] A scientific look into the dynamics of the shot cycle of three spring-piston airguns

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Hector J Medina G
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Not an April's Fools joke.

This will be a NINE part series.

We use three of the best recoiling spring-piston rifles ever made.

We will publish one part every two weeks.

https://www.ctcustomairguns.com/hectors-airgun-blog/shot-cycle-dynamics-in-3-spring-piston-airguns-preface

Hope you all enjoy!

 

 

HM


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Steve in NC
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Posted by: @jim-in-uk

Start-up ritual for every accelerometer session. Place the accelerometer horizontal and check that it reads 0v. Place it vertical and remind yourself (if you need reminding) how many volts equals one G.

It's difficult to get wrong, Steve, even for me. 

I'm keeping an open mind and trying to dream up a way of accurately recording peak pressure or temperature, or piston stroke, which may be the easiest. 

Well Jim, while I admire the elegant simplicity of the theory of your calibration method, I'm not so sure about the practice side.

A long (and sometimes even allegedly productive) career involving frequent hand-to-hand combat with uncooperative instrumentation taught a number of hard-learned lessons.

One of these was that attempting to calibrate a sensor to a signal that is less than 1% of its full-scale range often runs afoul of any number of unexpected nonlinear complications: e.g., hysteresis.  Not saying that happened here, but I'd worry.


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Jim in UK
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Posted by: @steve-in-nc
Posted by: @jim-in-uk

Start-up ritual for every accelerometer session. Place the accelerometer horizontal and check that it reads 0v. Place it vertical and remind yourself (if you need reminding) how many volts equals one G.

It's difficult to get wrong, Steve, even for me. 

I'm keeping an open mind and trying to dream up a way of accurately recording peak pressure or temperature, or piston stroke, which may be the easiest. 

Well Jim, while I admire the elegant simplicity of the theory of your calibration method, I'm not so sure about the practice side.

A long (and sometimes even allegedly productive) career involving frequent hand-to-hand combat with uncooperative instrumentation taught a number of hard-learned lessons.

One of these was that attempting to calibrate a sensor to a signal that is less than 1% of its full-scale range often runs afoul of any number of unexpected nonlinear complications: e.g., hysteresis.  Not saying that happened here, but I'd worry.

I didn't know that, Steve. Might comparing the displacement from the accelerometer data with that from the linear generator (scaled to fit) be a reasonable check for nonlinear issues? 


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Steve in NC
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Posted by: @jim-in-uk

@steve-in-nc

Way above my head, but thanks for the explanation.

I'm sorry, Jim.  Please excuse my incoherent babbling and let me try again.

The question was whether chamber pressure averaged over an estimated 3ms of pellet bore transit time is at least high enough to equal 11fpe / 335mm / pellet-base-area = 407psi.

To answer it, I averaged the 148 g-force readings (i.e. from 1.5ms prior to the pressure peak to 1.5ms after) and got 31mV.  I then divided that result by 72.2mV, the amplitude of the peak pressure g-force, got 43%, and multiplied that by the previously calculated 594psi.

Voila!  The maximum possible average pressure over the 3ms and 11 inches of pellet acceleration, assuming it to be centered on the peak for the highest theoretically possible ME:  255psi.

Which is only enough for 7fpe.

Better?

(edited for multiple typos)


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Jim in UK
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@steve-in-nc

Much better, thanks, Steve, though if I had to describe your post, I would never use the term 'incoherent babbling'. 


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Steve in NC
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Posted by: @jim-in-uk

I didn't know that, Steve. Might comparing the displacement from the accelerometer data with that from the linear generator (scaled to fit) be a reasonable check for nonlinear issues? 

Any sort of cross-check might be revealing.


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Steve in NC
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Posted by: @jim-in-uk
Posted by: @steve-in-nc
Posted by: @jim-in-uk

I didn't know that, Steve. Might comparing the displacement from the accelerometer data with that from the linear generator (scaled to fit) be a reasonable check for nonlinear issues? 

On the subject of accelerometer nonlinearity, awhile back you posted this interesting plot, which seems to show both red and blue post-firing-cycle "final" positions accelerating away at approximately the same (albeit in opposite directions) 2mm/s/10ms = 0.02g.   Failing to integrate a closed trajectory back to zero is just the sort of nasty trick nonlinearity can play.

image

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Steve in NC
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I'm indebted to Jim in UK for this lovely example of what an inductively sensed recoil plot ideally looks like when the sensor is rigidly attached to the rifle.  Note in detail the respective shapes of the leading and trailing edges of the initial recoil velocity peak, especially the practically vertical rise of the latter due to violence of piston bounce deceleration.

Thanks, Jim.  You set the standard.  Of course that's only fair -- since you invented the thing!

image

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Steve in NC
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John,

In your description of the recoil measurement apparatus, you say...

...for an air rifle one can neglect the momentum of the pellet, which in this case is around 40 times smaller than the momentum of the piston or rifle.

On first reading, this made perfect sense, because in typical shooting, you certainly can.

But just now I got to pondering if, in the context of the method of sensor calibration you're using -- in which the ratio of sensor signal to sled velocity is calibrated using the total displacement of the sled -- you really can safely neglect the pellet's momentum?

Please check my arithmetic.

In the course of firing a round, your 18.1lbs =  126,700 grains of rifle+sled will expel ~8 grains of pellet at ~250m/s + ~1 grain of superheated air muzzle blast at ~500m/s.  Net velocity imparted to sled will therefore be...

V = (8 x 250 + 1 x 500) / 126700 = 0.0197m/s = ~20mm/s

Unless I slipped a decimal place somewhere, it would seem that, since the total displacements you measure and use for calibration are typically less than 10mm, the potential for pellet-related recoil to move the sled that far in only half a second might be a bit more than you can afford to "neglect."

In fact, I think this ~2mm/100ms residual velocity can actually be seen in some of your position plots.

image

 

If the sled continued to coast for a significant fraction of a second, and therefore potentially several mm after the end of data recording, what effect would this have on your calibration calculation?

Wouldn't it result in a significant over-estimation of the calibration constants for both velocity and acceleration?


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Steve in NC
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Posted by: @steve-in-nc
 
Interesting.  The TX200 MkIII I'll be testing soon (my wire arrived!) all-up weight (it wears only a small scope) is 11lbs 6oz.  

92g x 11.375lb = 1067lb  1067lb x (25mm /2/25.4)^2 x Pi = 812psi

Thanks to Jim-in-UK's eagle eye catching it, please note that this calculation is wrong.  I multiplied acceleration force by piston area instead of dividing.  Duh!  It should be:

92g x 11.375lb = 1067lb  1067lb / ((25mm /2/25.4)^2 x Pi) = 1402psi

Thanks, Jim!


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Steve in NC
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Progress!   The coil is wound and tested -- worked out to about 200' and about 1500 turns of 40AWG, secured with a bit of Teflon pipe tape.

The DS212 scope is on order.

image

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Steve in NC
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Posted by: @johnc
...

I'm glad to see that you're building your own setup. I'm sure that you've already thought of this, but please be aware that pc sound cards are ac-coupled, so you won't be able to use the calibration technique that I described in Ch. 1.

Best wishes,

John

I'm also considering possible ways to correct the AC coupled data, depending on what the low frequency response of my computer's audio h/w actually turns out to be.

The simplest model of a 20Hz -3dB per octave rolloff is a single-pole RC 8ms timeconstant with a step-function response such that... 

Y(t) = Y(0)exp(-t/0.008)

That could theoretically be corrected back to DC with an exponential summation.

But as the wise(ass) man said: 

In theory there's no difference between theory and practice. 

But in practice, there IS!

 

John,

I think I may have made good on that conjecture, making it possible to acquire DC data with a PC mic input with just a relatively simple post-acquisition spreadsheet mathematical massage.

Please consider...

Ai: (i = 1 to N) Array of N acquired AC-coupled input data.

t = Time between input samples (typically 1 / 44kHz for digital audio)

T = RC timeconstant of the audio input, typically T = 1 / (2PiFo) where Fo = low frequency -3dB cutoff = 8ms for 20Hz

Di: (i = 1 to N) = Array of DC corrected output data.

Then Di = Ai + SUM(A1:Ai) * (e^(t / T) - 1)

Below find an example of the algorithm working on a step function.  Blue is the raw Ai data representing what's left of a stepped signal after passing through AC coupling, red is the corrected Di array produced by the algorithm, identical to the original signal.

So -- maybe a scope isn't necessary to acquire DC data after all, which might move participation in this project within the bounds of enthusiasm of even more potential participants. 

image

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JohnC
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@steve-in-nc

Hi Steve,

Do you have any way to put a square wave with with ~10ms period into your pc audio input? If you had a function generator or maybe another pc where you use the output of the audio jack, you could characterize the ac coupling of your audio input? If you can fiddle with the parameters got get the square wave back, then the problem is pretty much solved. One challenge with modelling is that you can't be sure exactly how and where your ac coupled pc input starts cutting out lower frequencies, so actually measuring the ac coupling response with a well-know input could help.

The DS 2212 scope will make things a lot more straightforward.

I agree that the sled is still moving after 0.1s and this most likely due to the recoil momentum opposing the pellet momentum, as you suggested. In principle the sled should keep moving back forever, but friction eventually wins. When I did the calibration by moving the sled by hand (fig. 1.7), I actually stopped the sled against a steel bracket, so I think the calibration is still reasonably good. I should have done some longer time scans to see where/when the sled stops moving. I don't think the sled moved much after 0.1s, but it certainly could have moved a few more mm. I'd be happy if the calibration was accurate to ~10%, but the it could have been a little worse, but not much worse. Again, the tests here are focused on comparisons of the behavior of three rifles, so I wasn't too concerned about absolute accuracy.

Best wishes,

John


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Steve in NC
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Posted by: @johnc

@steve-in-nc

Hi Steve,

Do you have any way to put a square wave with with ~10ms period into your pc audio input? If you had a function generator or maybe another pc where you use the output of the audio jack, you could characterize the ac coupling of your audio input? If you can fiddle with the parameters got get the square wave back, then the problem is pretty much solved. One challenge with modelling is that you can't be sure exactly how and where your ac coupled pc input starts cutting out lower frequencies, so actually measuring the ac coupling response with a well-know input could help.

The DS 2212 scope will make things a lot more straightforward.

I agree that the sled is still moving after 0.1s and this most likely due to the recoil momentum opposing the pellet momentum, as you suggested. In principle the sled should keep moving back forever, but friction eventually wins. When I did the calibration by moving the sled by hand (fig. 1.7), I actually stopped the sled against a steel bracket, so I think the calibration is still reasonably good. I should have done some longer time scans to see where/when the sled stops moving. I don't think the sled moved much after 0.1s, but it certainly could have moved a few more mm. I'd be happy if the calibration was accurate to ~10%, but the it could have been a little worse, but not much worse. Again, the tests here are focused on comparisons of the behavior of three rifles, so I wasn't too concerned about absolute accuracy.

Best wishes,

John

Hi, John,

I couldn't agree more that investing in a scope would avoid the fiddly bits of making a PC audio input do the job.

However, I love your and Hector's model of crowd-sourced every-man's DIY springer science so much that the goal of paring the required investment down to the absolute bone is maybe worth working for.  I suspect there are folks out there who would like to contribute, but find a potential investment in the $100s hard to justify for instrumentation they'll use only once.

Anyway, that's the ideal I'm chasing.

Meanwhile, if you get a chance to rerun some of your calibration scans to times long enough to let the sled coast to a friction-limited stop, that would be interesting.


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JohnC
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@steve-in-nc

I agree that using a pc audio input would make this kind of testing a lot more accessible. It's really cool that you can reconstruct the dc coupling signal! I'm looking forward to trying it on my pc using a function generator.

The oscilloscope is nice for looking at more channels. I'm now measuring barrel orientation as a function of time and am using all four channels on a scope.

Best wishes,

John

 


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Steve in NC
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Posted by: @johnc

@steve-in-nc

I agree that using a pc audio input would make this kind of testing a lot more accessible. It's really cool that you can reconstruct the dc coupling signal! I'm looking forward to trying it on my pc using a function generator.

The oscilloscope is nice for looking at more channels. I'm now measuring barrel orientation as a function of time and am using all four channels on a scope.

Best wishes,

John

 

John,

Thanks for the kind remark!  There's supposedly a dual channel function generator built into the sound card 'scope freebie s/w I'm using, and if I can figure out how to get it to output actual signals while the microphone input is also active (no idea why that doesn't seem to want to work!), I certainly plan to do the actual experiment too, instead of only simulating it.

So long as this is a realistic model of the mic input...

image

...it's prettymuch guaranteed to work given the right T value, but then there's that theory vs practice thing again!

When you give the DC reconstruction expression a whirl, if there's any issue with Excel run times (I assume you're spread-sheeting it) with big arrays, please note that (e^(t / T) - 1) is a constant and so need be calculated only once, and SUM(A1:Ai) would probably run a little quicker if allocated its own column and having the Ai data added one at a time as needed.

Of course, with a fast laptop, it all may be academic.

KR,

Steve


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Steve in NC
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Posted by: @johnc

@steve-in-nc

Hi Steve,

...When I did the calibration by moving the sled by hand (fig. 1.7), I actually stopped the sled against a steel bracket, so I think the calibration is still reasonably good...

John

John,

Excellent point!   I apologize for missing that element of your description of your method and apparatus, and agree that it renders my comment about pellet momentum's effect on calibration mostly moot.

For some reason I imagined you were re-doing the total displacement calibration method for each gun individually.

Steve


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Steve in NC
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Posted by: @steve-in-nc
Posted by: @johnc

@steve-in-nc

I agree that using a pc audio input would make this kind of testing a lot more accessible. It's really cool that you can reconstruct the dc coupling signal! I'm looking forward to trying it on my pc using a function generator.

 

image

 

image

Blue:  All was left by the ADC from a 100Hz squarewave.

Red: Numeric reconstruction of same.

Definitely not perfect.  The ADC low-end cutoff turned out to be a disappointingly high 100Hz = 1.6ms, so the necessary correction is correspondingly extreme, but maybe good enough?


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Steve in NC
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Thought for the day: This digital springer stuff ain't as easy as it looks! 

First (failed -- but with an explanation!) attempt to acquire a recoil-O-gram.

Equipment...

1. 11lb 6oz (as shown) 16fpe (955fps with CPLs) TX200

2. Dynamic pickup, elegantly zip-tied to an (NIST - traceable!) 2kg (calibrated!) brick, hooked to my long-suffering Dell laptop.  Note the aluminum pushrod reaching under to scope to contact the mount directly.

3. Wildly over-ranged PC ADC!  I'm just lucky it didn't fry the thing.

4. Next job:  A bit of signal attenuation!

image
image
image

 


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Steve in NC
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PS: The measured (Lyman digital trigger pull gauge) force required to overcome friction and make the gun slide on the rug is 3lbs 8oz, roughly 1/3 of its 11lbs 6oz weight.  Consequently, measured accelerations can be expected to be understated by ~1/3g.

Just in case anyone was interested in this aspect of the "free-sliding" approach.


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Steve in NC
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Raw AC-coupled scope trace with 150k signal attenuation resistor added in series with ADC input for ~30:1 (29.5dB) attenuation.

tx200c

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Steve in NC
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Posted by: @steve-in-nc

Raw AC-coupled scope trace with 150k signal attenuation resistor added in series with ADC input for ~30:1 (29.5dB) attenuation.

tx200c

DC corrected velocity plot in blue, Acceleration plot (g-force) in black.

image

Expanded time axis in vicinity of piston bounce...

image

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Hector J Medina G
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A day late!

Sorry 😏

Chapter 4 is here: Swapping powerplants between an LGU and an LGV:

https://www.ctcustomairguns.com/hectors-airgun-blog/shot-cycle-dynamics-in-3-spring-piston-airguns-chap-4  

 

Hope you enjoy!

 

 

 

 

 

HM


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Steve in NC
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Position:  Vertical axis is mm of displacement (recoil) toward the butt, horizontal axis seconds.

image

I don't recall anyone ever commenting on how remarkable it is that the instantaneous maximum rearward recoil position of the gun is farther back (here ~1.5mm farther) than the rest position, even though it's the latter that represents the ultimate rest of the piston at its farthest forward position in the tube.  If we focus solely on the piston's mass as the source of momentum pushing the gun back, this shouldn't be possible.

But of course, the piston isn't the only internal mass that moves forward as the gun moves backward.

In fact this proves (if proof were necessary) that at the instant of bounce, the spring comes totally free of the rear guide and stacks up behind the piston, adding its mass and momentum to the piston before later relaxing and allowing the gun to partially  re-rebound forward.

Have we discussed this peculiar sequence before and I missed it?


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Steve in NC
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I've mentioned before Jim-in-UK's unparalleled expertise in interpreting plots of dynamically acquired spring recoil data.  Today, after briefly inspecting an example of my recent efforts to acquire them, he said:  "I'm wondering what the notch approaching peak velocity is?"

image

Good question!  After pondering it for awhile, I have a theory.

All my spring guns are break barrels -- except the TX.  And in the TX, unlike the BBs, besides piston and spring, there's an extra major internal component with significant mass capable of pressure-related movement.  Wait for it...

The compression tube.

I'm theorizing that "the notch" is caused by movement of the tube as rising chamber pressure forces it forward to impact with the breech.

Plausible, Jim?

If so, this is perhaps a good example of the kind of detailed insights into springer physics that are possible with a dynamic sensor properly coupled to a spring-piston action.


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Jim in UK
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You could test one of your break barrels and see if the notch disappears, Steve.


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Steve in NC
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Posted by: @jim-in-uk

You could test one of your break barrels and see if the notch disappears, Steve.

What?!   And put my beautiful theory at risk of contradiction?

But all seriousness aside, of course I do plan to run a few BBs thru, but first I'll be rigging a haywire (literally) arrangement where one of the sensor-signal carrying conductors will pass in front of the TX muzzle so that it will be cut by the pellet within microseconds of the latter's exit.

Therefore, if exit really does occur before bounce, the bounce signal won't be seen at all.

And vice-versa.


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Steve in NC
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16fpe TX200 calibrated G-force acceleration plot. 

 Goal for today:  Pellet exit time measurement.

image

 


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Steve in NC
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Pellet Exit Time Experiment

The rig:  Aluminum foil tape carrying Linear DynamicSensor signal to laptop audio ADC at muzzle of 16fpe (953fps with CPLs) long-stroke TX200, where pellet must cut it at the moment of exit.

image

...Before...

image

...After...

image

 

...The result:  Loss of signal (hence pellet exit) at ~1ms AFTER piston bounce.  

image

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Steve in NC
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Afterthought:  You might want to subtract 300us of so to allow for the fact that the length of the TX baffled shroud separates the end of the actual bore from where I could place the foil.


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Steve in NC
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First break barrel:  14fpe RWS94 (Cometa 400)

8lbs 4oz, 9mm recoil distance, very twangy

IMG 3319
image
Cometa1

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Steve in NC
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Another Breakbarrel: 13fpe Gamo Shadowmatic

843fps = 12.9 fpe with 8.2gr Meisterkugelns, 9lbs 2oz as tested, 7mm final displacement, VERY twangy!!

Shadowmatic

 

temp

 

image

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Steve in NC
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In case anyone's wondering about the photo above in which I've connected the recoil sensor to a plastic trigger guard, which would seem a terrible idea from earlier discussions about the necessity for rigid connections between gun and sensor, let me explain why it's okay.

The total moving mass of the sensor (aluminum pushrod, magnet, and spring) only adds up to 7 grams.  So even hundreds of g's of acceleration require only a few pounds of force to make the sensor accurately track the gun's motion.

Note how this differs from John and Hector's instrument where their kilogram sled would need 100s of pounds of force to accomplish the same task.

In the free-sliding case, just a plastic trigger guard is rigid enough.


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Steve in NC
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Third Breakbarrel: 15fpe Webley Tomahawk

Thought for the day:  Breakbarrels are peculiar critters -- especially when you measure the motion of the breech block!

image
image
image

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Hector J Medina G
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Comparing SuperLube to Krytox.

Chapter 5 is here:

https://www.ctcustomairguns.com/hectors-airgun-blog/shot-cycle-dynamics-in-3-spring-piston-airguns-chap-5

Hope you enjoy!

 

 

HM


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airgunwizard
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Thank you Hector for your hard work and for presenting this !

A true learning experience.


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Hector J Medina G
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@airgunwizard

Thank YOU for reading!

 

Thanks should really go to John Cerne and Yogi, and also to Steve Herr.

I am merely the "publisher"

 

😉

 

Keep well and shoot straight!

 

 

 

 

 

HM


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Hector J Medina G
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Chapter 6 is here, analyzing the effect of rifle weight on precision and accuracy:

https://www.ctcustomairguns.com/hectors-airgun-blog/shot-cycle-dynamics-in-3-spring-piston-airguns-chap-6

Hope you enjoy!

 

 

HM


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Hector J Medina G
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Chap 7 is here, and we look at how power level affects different guns.

https://www.ctcustomairguns.com/hectors-airgun-blog/shot-cycle-dynamics-in-3-spring-piston-airguns-chap-7

 

Hope you enjoy!

 

 

 

 

HM


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Hector J Medina G
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Chap 8 is here:

https://www.ctcustomairguns.com/hectors-airgun-blog/shot-cycle-dynamics-in-3-spring-piston-airguns-chap-8

John Cerne shows us now how the distribution of weights along the barrel affect precision and accuracy, and concludes that manufacturers have "broader" priorities than shooters.
Enjoy!

 

 

HM


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Steve in NC
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Thank you, Hector, for another interesting article.  I have a question.

In the article, John makes this intriguing observation about the effects of removing the endcap from his LGU's moderator, "This greatly increased the report of the rifle..."

I wonder what this change in the sonic environment of the rifle might might imply about changes in near-muzzle airflow as it moves along with the pellet?  In particular I wonder about changes in airflow with and without the restriction of the endcap, how said changes might have contributed to the changes in POI that John observes, and why barrel vibrations were the only possible causation considered?

Now I hesitate to mention the research in this area that the Cardews included in Trigger to Target, because you've repeatedly said how "dated" you regard their work to be.  But the effects of near-muzzle airflow on the flight of the pellet is a topic they treat in some detail.  Recommended reading.

Please note, for example, this sequence from page 197 in which near-muzzle airflow is shown actually upsetting the pellet.  The likely effect on accuracy of changing anything that might affect said airflow (e.g., removing a moderator baffle) is, I think, pretty obvious.

image

 

 


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Hector J Medina G
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@steve-in-nc 

The air flows at JUST the moment of pellet release are a whole different can of worms from the barrel vibrations, yes you are right. During the preparation stage of the article I offered two different "devices" to Jhon: a baffle series to be housed in the cavity, and a "floating weight" that was designed to reduce the barrel vibrations. He opted for none, but still I sent him a "floating weight" because I had had good results in at least 4 LGU's previously tuned. 

John DID test the device, but he still opted to keep his "no cap" arrangement as the "best possible results at the target" option. So, what he presented is what he believes to be the MAIN effect.

Now, to explain why the process of pellet release to vibrations of the barrel timing needs to be INDIVIDUAL to the gun lie VERY deep in the making of a barrel. But to explain it in just a few words: The process of rifling a barrel introduces radial stresses in the barrel being made that are NOT uniform, nor equal to all barrels. So, EACH barrel will vibrate differently from all other barrels produced. In SOME PCP's you have the option of "indexing" a barrel, not in spring-piston airguns.

In the specific case of the LGU, the way it was explained to me by the designer, was that the cavity had been devised (he didn't say "designed", so for a German engineer that means that it was a trial and error procedure) as a "Resonant Cavity". A resonant cavity is a cavity that uses the length of the longitudinal air wave to either amplify (constructive interference), or reduce (destructive interference)  the sound signature.

Why use that in the LGU?  Two reasons:

Commercial.-MANY countries forbid the use of sound moderators/baffled devices in ALL guns (airguns included) and, so, the use of ANY baffled device would have reduced the overall possible market for the rifle.
It was also a push along what SHOULD have been the "Leit Motif" of the gun series:  "The sound of silence".

Technical.- In a CONSTRICTED environment, the air flows are not exactly as the Cardews published them, there is a speed of flow where a cylindrical column of air can gather enough difference in speeds (as the surrounding air is being held by the turbulent flow and the cap, and the caliber sized column is not) that it "punches" a core through. So the pellet is not really travelling through the turbulent flow of the "mushroom" generated by the conditions developed under "open air" situation.

Now, it is true that by REMOVING the front cap John gave back to the air flows one degree of freedom they had lost under the original design intent. But evidence suggests that while that definitely had some effect, the overall effect of removing the weights at the end of the "barrel/cantilever beam" reduced the excursions produced by vibrations even more.

Now, if we were to talk about the LGV, then  the conditions are completely different and you (and the Cardews) are absolutely right. It doesn't help the gun's accuracy and precision that, even with the 1" bore  (approx.), the LGV still has a LOT of swept volume for the 12 ft-lbs of the major market objective and, so, the LGV is one of those guns that responds FANTASTICALLY well to the addition of an air stripper at the muzzle. For most of the UK shooters, the moderators they use perform the same basic work as a stripper, plus the added work of containing the high pressure air release to reduce the sound signature.

Yes, the EXACT moment when the pellet is released from the rifling is a crucial moment to precision and accuracy, but that is true for ALL gas/pressure driven projectiles and was established by Greener MANY years before the Cardews.

It is also the DRIVING reason behind getting the BEST possible "crown" you can in a barrel, as well as getting the most uniform/flat ring of release projectiles you can.

In the Cardews' picture you illustrate, it is clear that while the pellet is being upset from its perfectly linear travel, the air flow (revealed by the "Schlieren-type" lines of shadow) also demonstrate that the air flow does not overtake the pellet. That WAS true in their days at their power levels. At current power levels and "pop/diesel gun" regimes. the air flows DO overtake the pellet and create a "mushroom" through which the pellet must travel. Again, this is why air strippers work, specially in PCP's that  use a TON of air for each shot, but also true for any airgun with a compression chamber bore larger than 20-23 mm's ID.

It is also the reason why the 34 EMS has threaded barrels 😉

Thanks for your comment, thanks for reading critically and in detail. Hope I have answered the question.

Keep well and shoot straight!

 

 

 

HM


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