Theoretical Maximum Velocity in a PCP



Author Topic: Theoretical Maximum Velocity in a PCP  (Read 46175 times))

Offline rsterne

  • Member 2000+fps Club
  • Bob and Lloyd
  • GTA Senior Contributor
  • *****
  • Posts: 21222
  • GTA Forums Person of the Year 2017
    • Mozey-On-Inn
  • Real Name: Bob
Re: Theoretical Maximum Velocity in a PCP
« Reply #440 on: January 11, 2019, 01:05:33 PM »
We aren't talking a low-mass, large diameter projectile here.... Look at the SD of a .45 cal lead ball compared to that of a ping-pong ball.... Comparing apples and lizards....  ::)

Removing the mass of the air from the barrel of a ping-pong ball cannon, and adding 15 psi to 80 (a 19% increase in pressure differential and therefore force). is a whole lot difference to removing the mass of air from the barrel of a Texan and increasing the pressure differential by 0.3%....  ;)

Bob
  • Coalmont, BC, Canada
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsenal:
1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine, 2260 HPA (37 FPE), 2560 HPA (52 FPE), .22 QB79 HPA, Disco Doubles in .22, .25 & .30 cal, "Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, 7mm, .308 & .357; Mk.III is .410 shotgun and .458 cal), .257 "Monocoque" Bench PCP, 6mm Regulated PCP and .257 Unregulated, Three BRods.

Offline jackssmirkingrevenge

  • Plinker
  • **
  • Posts: 234
  • yes
    • The Spudfiles Forum
  • Real Name: Jack
Re: Theoretical Maximum Velocity in a PCP
« Reply #441 on: January 11, 2019, 01:38:31 PM »
Removing the mass of the air from the barrel of a ping-pong ball cannon, and adding 15 psi to 80 (a 19% increase in pressure differential and therefore force). is a whole lot difference to removing the mass of air from the barrel of a Texan and increasing the pressure differential by 0.3%....  ;)

No doubt about that, but my understanding is that it has more to do with removing the air drag that the pressure differential, not sure if this has been mentioned before as I have not read through the whole thread.

If we look at Light Gas Guns used for hypervelocity impact testing, they use a powder charge to compress a cylinder of hydrogen or similar light gas to hundreds of thousands of pounds of pressure, and yet they still bother to evacuate the barrel even though the pressure differential is infinitesimal.

There are other reasons to do this of course, if you're simulating an impact in outer space then you want it to happen in a vacuum to be as close as possible to the actual conditions.  Also at velocities of 7 kilometers per second (almost 23000 fps :o ) then your projectile heating up with air friction also becomes an issue.

I did however dig up a report on "TWO STAGE LIGHT-GAS GUN INSTALLATION FOR HYPERVELOCITY IMPACT STUDIES" and it clearly states on page 6 of the report (page 14 of the pdf):

Quote
The launch tube is evacuated to minimize air resistance during acceleration of the projectile.



  • Quebec, Canada
"You have to make many weapons, because this field is long and short life"

Offline MJP

  • Member 3000+Fpe Club
  • Expert
  • *****
  • Posts: 1380
  • I'll make it real. For me.
  • Real Name: Marko
Re: Theoretical Maximum Velocity in a PCP
« Reply #442 on: January 11, 2019, 02:28:05 PM »
Ping bong ball is a whole different matter, look at the surface area for the pressure to push on considering the weight.  Remove the atmospheric pressure from one side you have a lot of energy right there.

And hyper velocity studies is another thing entirely, they want all the speed they can get and effort or money is not the problem. Velocity is the key there, and air resistance becomes a major effect at those speeds.

Marko
  • Finland
Impossible just takes a little bit longer to achieve.

Offline Sfttailrdr46

  • Of all the things I have lost I miss my mind the most
  • GTA Moderator
  • GTA Senior Contributor
  • *****
  • Posts: 14008
  • Think first then hit send
  • Real Name: Don
Re: Theoretical Maximum Velocity in a PCP
« Reply #443 on: January 11, 2019, 02:40:58 PM »
 :D My mentioning the Ping Pong ball AG was only because they did use a vacuum in the front of the ball to help achieve higher FPS not to compare apples to walnuts
  • Long Island N.Y.
AA S510 Xtra Fac .177 RH Walnut FS
Rainstorm II .22 AWESOME Rifle
Air Speed .25 Smile Machine
FX Crown .22 w/600 mm Barrel ordered
Gamo Whisper Fusion .177
Gamo Swarm Maxxim .22
Marauder GenII .30  Boyd's TH 100+ fpe FS
RWS D460  .177  
PP700 SA ,22 PCP pistol W/Rocker1 LDC & Red Dot
CP2 .22 Pistol/Carbine
SPA Varmint .177
Freedom 8 & Guppy CF Tank & 45 min SCBA
 https://www.zeemaps.com/map?

Offline MJP

  • Member 3000+Fpe Club
  • Expert
  • *****
  • Posts: 1380
  • I'll make it real. For me.
  • Real Name: Marko
Re: Theoretical Maximum Velocity in a PCP
« Reply #444 on: January 11, 2019, 03:16:09 PM »
But it was a good idea, unfortunately for us the heavy and small projectile kind of kills the idea.

Marko
  • Finland
Impossible just takes a little bit longer to achieve.

Offline rsterne

  • Member 2000+fps Club
  • Bob and Lloyd
  • GTA Senior Contributor
  • *****
  • Posts: 21222
  • GTA Forums Person of the Year 2017
    • Mozey-On-Inn
  • Real Name: Bob
Re: Theoretical Maximum Velocity in a PCP
« Reply #445 on: January 11, 2019, 03:45:47 PM »
Light gas guns, which use an explosive charge to fire a piston to Adiabatically compress a light gas (H or He) and achieve velocities up to Mach 5 of that gas at those elevated temperatures and pressures are NOT a PCP.... This thread has been sidetracked there before, please start a thread on light gas guns if you wish to discuss them.... The "Back Room" might be a suitable Gate?....

The ability to accelerate a projectile with a limited pressure differential is closely tied to the Sectional Density.... The SD of a 144 gr. .457 cal roundball is 0.098.... A ping-pong ball weighs 2.7 grams (41.7 gr.) and has a diameter (caliber) of 40 mm (1.57"). Therefore the SD is 0.0024.... making it 41 times easier to accelerate.... Without the mass of the air in front of it, a pressure differential of just 110 psi will provide the same "g" of acceleration as would 4500 psi in the Texan....  :o . No wonder ping-pong ball cannons, with a barrel many feet long, can drive a ping-pong ball supersonic....  8)

Bob
  • Coalmont, BC, Canada
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsenal:
1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine, 2260 HPA (37 FPE), 2560 HPA (52 FPE), .22 QB79 HPA, Disco Doubles in .22, .25 & .30 cal, "Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, 7mm, .308 & .357; Mk.III is .410 shotgun and .458 cal), .257 "Monocoque" Bench PCP, 6mm Regulated PCP and .257 Unregulated, Three BRods.

Offline jackssmirkingrevenge

  • Plinker
  • **
  • Posts: 234
  • yes
    • The Spudfiles Forum
  • Real Name: Jack
Re: Theoretical Maximum Velocity in a PCP
« Reply #446 on: January 11, 2019, 05:08:43 PM »
This thread has been sidetracked there before, please start a thread on light gas guns if you wish to discuss them...

That was not my intention, I just wanted to make the point that they are "prior art" in the field of gas based acceleration and they incorporate evacuated barrels not for the purposes of creating a pressure differential but to prevent acceleration being limited by the atmosphere.

Since the vacuum apparatus adds a complex and expensive element to the device, then including it must mean that the dividends are significant in terms of increased acceleration, beyond what is gained by simply removing the mass of the air in the barrel.
  • Quebec, Canada
"You have to make many weapons, because this field is long and short life"

Offline TPL

  • Member 3000+Fpe Club
  • Marksman
  • ***
  • Posts: 310
  • Real Name: Timo
Re: Theoretical Maximum Velocity in a PCP
« Reply #447 on: January 12, 2019, 07:44:14 AM »
With AG velocities there is absolutely very small effect due to air in front of the projectile. Maybe in light gas guns their purpose of vacuuming is decreasing barrel stress to minimum yet I haven't seen nor didn't even know it has done. Still atmospheric air pressure is there right after muzzle.

Anyway that video claims barrel vacuuming produces 13.6 times the energy. That's well enough to me to skip the whole statement as BS. Actually I would be sceptic with 10% increase.

Besides, this guy is an expert in vacuuming:  ;D



I'm a bit disappointed for not to see the result of that experiment.
« Last Edit: January 12, 2019, 07:57:15 AM by TPL »
  • Tampere

Offline jackssmirkingrevenge

  • Plinker
  • **
  • Posts: 234
  • yes
    • The Spudfiles Forum
  • Real Name: Jack
Re: Theoretical Maximum Velocity in a PCP
« Reply #448 on: January 12, 2019, 10:03:58 AM »
Anyway that video claims barrel vacuuming produces 13.6 times the energy. That's well enough to me to skip the whole statement as BS.

If that's what's being claimed then the statement can be dismissed out of hand.
  • Quebec, Canada
"You have to make many weapons, because this field is long and short life"

Offline TPL

  • Member 3000+Fpe Club
  • Marksman
  • ***
  • Posts: 310
  • Real Name: Timo
Re: Theoretical Maximum Velocity in a PCP
« Reply #449 on: January 12, 2019, 12:06:30 PM »
I think we all know how to do it. Place your muzzle touching chono and there it is, a world record of a kind you would like to achieve. No matter of error message, it is not that important when we are doing a WR.  :P
  • Tampere

GTA - What's been your success with air gun target practice?
 

Thank you for Supporting GTA!
Sponsored Ad: