.458 big bore mule test bed project (video added)

[lloyd-ss]

Interesting for sure . I have a mind like yours so bare with me .  How is this being calculated ? Sensor at points in the barrel ? Marvin

Marvin,

The data table is from my actual test shots.  (edit- added this sentence)

The graphs are from an excel spreadsheet program that I developed that calculates the travel of the bullet through the barrel.  The formulas used are fairly straightforward, but the equations that account for the losses are pretty involved.  I have been comparing what the calculator gives me to real world data, and refining the calculations for several years.  It's about at the point where if I have a sampling of data from a gun, I can calculate what it will do with other pressures, bullet weights, barrel lengths, tank volumes, etc.

The inputs to the program include: bore, reservoir volume, valve dwell time, barrel length, transfer port volume, bullet weight, tank starting and ending pressure (for the shot).  For system losses, it accounts for the mass of the air column behind the bullet, the bullet drag in the barrel, the bullet breakaway force at the breech, and the system mechanical efficiency.  It's a great what-if calculator.  For example, just by looking at the graphs, you can predict what would happen if you shorten the barrel.  Currently, it's 36", and I am definitely going to shorten it.  That last 6" of barrel doesn't add much to the energy of the 230 gn bullet.  It adds a little more to the 405 gn, though.

I hope that helps. My setup has an accurate digital pressure sensor, valve timing control, chronograph, and those are all hooked up to a laptop through a data acquisition program.  It works pretty well.

Lloyd

  

[melloroadman]

Lloyd please under stand I am not trying to find fault in this . Just understanding . I do not know if you or anyone took the time to read about the authors of From Ingot To Target but Glen E. Fryxell has a strong back ground . This info is showing what he has stated in his words which I believe as well to have substance . About the G force to psi is there away to convert ? Marvin

[rsterne]

Interesting comment from another forum about a Daystate Electronic (applies to the Rogue)

We may be looking at the future of air rifles, once they are operated by computer they can easily be configured for the velocity laws of any country just by changing a chip. So in Canada we could have 2 chips one non PAL and one PAL. Before you say that won't work because it would be too easy to update to a more powerful rifle, it is easy to lock a particular rifle (computer) to a specific chip only available at the factory. The price could even drop because a manufacturer would only need one main rifle and just change computer chips for desired performance.

Bob

[Butcher45]

This thread is simply amazing....."Technical Thread of the Year/Decade" type stuff.  The power you are getting on those low psi fills is staggering.....a hand-pumpers dream (if a pump will work with this set-up)!

I need to dedicate an entire evening to digest all of this before I comment further.....just haven't had the kind of time that is called for to do so.

Awesome stuff Lloyd!

[jetmangd]

LLoyd-SS,
              Wow, Just Amazing with all of the posted Stats on your chart, However shot # 9 is so Impressive with a Staggering
              706 FT/LBS with a 405 Grain Lead Bullet Traveling at a Very Respectful 886 FPS. Wow, LLoyd you are making & keeping
              this thread so Exiting and Awesome for us all to read and To be able to follow each and every step of the way with
              you. This is just so Cool to Read every day and see the changes. Thank you LLoyd.



                                                                               Jetman.
             

[lloyd-ss]

Lloyd please under stand I am not trying to find fault in this . Just understanding . I do not know if you or anyone took the time to read about the authors of From Ingot To Target but Glen E. Fryxell has a strong back ground . This info is showing what he has stated in his words which I believe as well to have substance . About the G force to psi is there away to convert ? Marvin

Marvin,
Quite alright.  I'll offer what I can.
 
I have run across Glen E. Fryxell in at least one place but have not studied what he has written.  I often start in a vacuum and look outside when I get stumped, so I am sometimes repeating other peoples efforts.  But as I've said in the past, I usually have to prove things to myself before I really trust it.

The spreadsheet that does the calculations is all my own with some enhancements based on suggestions from a few folks. It's pretty much classical mechanics using the power of the spreadsheet for repetitive calculations.

Regarding your question about the relationship between psi and acceleration, it's yes and no.
Taken at the basic equation, Force = mass x acceleration, or switched around to solve for acceleration, a = F/m, if the force against the base of the bullet is kept constant, the acceleration will stay constant.  The force on the base of the bullet is equal to area x psi, but as the bullet travels down the barrel, the volume of the tank is increasing, so the force is dropping off.  Then when the valve shuts, the force drops off even faster.  Also, as the bullet travels out the barrel, the mass of the column of air behind it has to be included with the weight of the bullet, because that column of air has to move as fast as the bullet (and 3000psi air is surprisingly heavy) so it is like the bullet is getting heavier as it travels down the barrel.  That's the tip of the iceberg, but I enjoy it.
Hope that helps a little.  I don't mind questions at all.
Lloyd

   

[lloyd-ss]

Interesting comment from another forum about a Daystate Electronic (applies to the Rogue)

We may be looking at the future of air rifles, once they are operated by computer they can easily be configured for the velocity laws of any country just by changing a chip. So in Canada we could have 2 chips one non PAL and one PAL. Before you say that won't work because it would be too easy to update to a more powerful rifle, it is easy to lock a particular rifle (computer) to a specific chip only available at the factory. The price could even drop because a manufacturer would only need one main rifle and just change computer chips for desired performance.

Bob

Bob,
yes, I tend to agree so long as the requirement/law  applies to energy and not velocity.  Put a lighter bullet in and you'll usually get more velocity.
Lloyd

[melloroadman]

Lloyd your charts show 8000 and 10000 G force . What would that relate to in terms of psi ? Is my question . Marvin

[lloyd-ss]

This thread is simply amazing....."Technical Thread of the Year/Decade" type stuff.  The power you are getting on those low psi fills is staggering.....a hand-pumpers dream (if a pump will work with this set-up)!

I need to dedicate an entire evening to digest all of this before I comment further.....just haven't had the kind of time that is called for to do so.

Awesome stuff Lloyd!

Thanks Butcher.   Yes, I hand pumped it from about 2500 to 3500 to get the high power shots because my tanks were low.  I think as all of you big bore folks know, "taming" a gun to get it to shoot at high pressure and low, and shoot big power and little power, is a real task.  You usually end up with a "blend."  This gun is working pretty good throughout the full range, but the real high power tests all the components.

I am learning an awful lot with this and having fun.  It keeps me off the streets, but at 60, what kind of trouble am I going to get into? LOL.
I really do promise to get a video of it in action, just have to fit it in and have my wife do the "filming."
Lloyd

[lloyd-ss]

LLoyd-SS,
              Wow, Just Amazing with all of the posted Stats on your chart, However shot # 9 is so Impressive with a Staggering
              706 FT/LBS with a 405 Grain Lead Bullet Traveling at a Very Respectful 886 FPS. Wow, LLoyd you are making & keeping
              this thread so Exiting and Awesome for us all to read and To be able to follow each and every step of the way with
              you. This is just so Cool to Read every day and see the changes. Thank you LLoyd.

                                                                               Jetman.          

Jetman,
Thanks very much.  I have to admit that those last 2 high power shots put a 100psi per minute leak in one of the seal sets and blew out the back end of the LDC, so I have some repairs to make.  Just another opportunity to fix the weak links.
Lloyd   

[rsterne]

Lloyd your charts show 8000 and 10000 G force . What would that relate to in terms of psi ? Is my question

The instantaneous pressure is on the other chart for the same shot.... Look at the same barrel position on both charts and you'll have your answer....

Bob

[lloyd-ss]

Lloyd your charts show 8000 and 10000 G force . What would that relate to in terms of psi ? Is my question . Marvin

Marvin,

I had to make 2 charts for each shot to keep it from getting to congested.  The green velocity lines kind of tie them together.

Charts 1 and 2 are both of shot number 9, the 405 gn bullet. (You have to watch scale you are reading with which curve.)
Chart one shows that the starting pressure is 3636psi at the beginning of the event and the acceleration peaks out at about 8000g after the bullet breaks loose from the breech. 

Charts 3 and 4 are of shot number 1, the 230 gn bullet.
That starting psi is only 2320 psi, but because the bullet is so much lighter (or technically, has so much less mass), the acceleration is about 10,000 g's when it breaks free.

Despite the difference in initial acceleration, both bullets end up leaving the muzzle at approximately the same velocity because the valve closes much more quickly with the lighter bullet.  You can see when that happens by the cusp in the blue PSI lines.

Hope that helps some more.
Lloyd

[melloroadman]

Not sure . I understand that the psi on the base of the bullet was 3636 . There was a launch with a force of 8000 G . At the peak of the launch or 8000 G on the nose of the bullet what was the pressure or pressure applied to the whole bullet . Marvin

[Jerry]

The nose of the bullet had 14.7 psia plus the dynamic pressure of moving the air out of the barrel.  The difference in pressure between that applied at the base and atmospheric pressure at the nose resulted in an 8000g acceleration.  The circumference of the bullet had no appreciable pressure applied as the barrel is not constricting, however, if the bullet material is soft enough to "obturate" the pressure the material applies to the barrel would be equally counter-acted or the barrel would expand...  A thin skirt lead pellet would in fact obturate some according to the "hoop" formula but a flat or conical or rebated base slug even of "soft" lead would not under this mild pressure.

Basically, it comes down to the pressure is not applied to the "whole bullet" or the bullet wouldn't move.

[Jerry]

BTW, Lloyd, awesome test data!

[melloroadman]

Thank you all . But I am being misunderstood . I have read and realize that it can not really be converted . Lloyd good luck with your sealing work . Keep up the good work .Marvin

[lloyd-ss]

Thank you all . But I am being misunderstood . I have read and realize that it can not really be converted . Lloyd good luck with your sealing work . Keep up the good work .Marvin

Marvin,
Maybe you are wondering how much "Force" is being applied to the base of the bullet?  At the very start it is 599 pounds of force which is the area of the bore x the psi ( .1647 sq ins  x 3636 psi).  Like Jerry said, because the muzzle is open, there is relatively no resistance (push-back)from the air in the barrel on the nose of the bullet.  The friction from the bullet rubbing the bore is only about 10 pounds with the particular bullets I was using.
Lloyd

[melloroadman]

Every one is right but what I wanted does not exist. Lloyd do not waste any more time on this . As I said I read up on G forces and see there is no answer to my question . Marvin

[Brushy Bill]

Amazing, the things coming out of "Lloyd's Laboratory"   

Glad to hear your still having fun.
Thanks for sharing with us.

[melloroadman]

Lloyd thank you again for your patience . What I ask was {And is there a way to covert the G forces if that is the proper term or a term I can use to psi }. The answer is no . G is a measurement of acceleration and the forces are felt as weight and cause stress and strain . Which I found out through research .
But your post has given me more insight as to what that bullet is going thought as it passes through the barrel . 10000 G is a lot of stress and stain . I had only been thinking is terms of pressure for the most part . Then there is also the rpm factor to consider as well . Marvin