Login    Register
User Information
Username:
Password:
We are a free and open
community, all are welcome.
Click here to Register
Sponsored
Who is online

In total there are 80 users online :: 5 registered, 0 hidden and 75 guests


Most users ever online was 155 on Mon Aug 15, 2016 1:40 am

Registered users: Bing [Bot], Google [Bot], Google Adsense [Bot], MSNbot Media, Yahoo [Bot] based on users active over the past 5 minutes

The Team
Administrators
Global Moderators
global_moderators.png CS

PCP cartridge, Mark 2

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
Sponsored 
  • Author
    Message

PCP cartridge, Mark 2

Unread postAuthor: LeMaudit » Wed May 06, 2009 9:52 pm

Here is a revision for my PCP cartridge. I followed your advices, removed the O-ring, increase the pressure by planning to use a shock-pump, decrease the chamber volume to less than 1 inch3 so I don’t have to pump too much (I’m lazy), and also adjusted the sizes to real material available at my closest Home-Depot and bicycle parts store :-D The tubing is now a standard 1 inch diameter with 7/8 internal hole (supposed to be 1200 psi rating), and 7/8” rubber washers with 3/8” hole seems readily available. A photograph of the Schrader valve I found at the bicycle parts store is on the drawing and seems perfect for what I want to do.

There was also a potential flaw in the previous design. Some links in the piston where loose, which was intended to avoid a vent hole. But I think it could potentially be dangerous if things are not aligned correctly when the pressure is build up, an accidental discharge could occurs. Of course I don’t want that! So I put back vent holes and a single piece piston. GGDT don’t show much performance lost anyway. And the mechanism will be more able to stand the pressure now increased to 400psi, which is about 200 pound (95 kg) for my internal 7/8” diameter. The piston is a bit more complicated to machine, but the rest is simpler so that’s okay for me. I also removed the internal O-ring for sliding the piston as I think I can machine a very good fit easily, and as soon as the firing starts there is no more pressure lost anyway thanks to the back rubber washer that seals everything.

So, here is a drawing again. If some of you care to comment and criticize, I’ll be more than happy. Unless you find a flaw, I think I will build this one for real.

With 400psi, which drop to 375 with the increase of the internal volume by 1/8” length when fired, GGDT gives me for a 8 inch length barrel a 14 ft*lb of energy, and 343 ft/s

I do intend to make two 12” extensions for the barrel, to change the handgun into a medium and long rifle. GGDT again gives me those figures:

20 inch barrel (8 + 12 extension) = 23 ft*lb, 430 ft/s
32 inch barrel (8 + 12 extension x2) = 27 ft*lb, 464 ft/s
Which is good as I’m still under the 500 ft/s Canadian law, but with great power! Well, at least I think it’s great ;-)

Anyway, back to the drawing board to prepare the rest of the design. I still don’t have the workshop installed, but when it’s done I promise you’ll see some shiny brass pieces :-D
  • 0

Attachments
big_ammo-mark2.gif
PCP Cartridge, Mark 2
big_ammo-mark2_ggdt_8inch-barrel.gif
8 inch barrel
big_ammo-mark2_ggdt_8inch-barrel.gif (23.21 KiB) Viewed 626 times
User avatar
LeMaudit
Donating Member
Donating Member
 
Posts: 665
Joined: Thu Apr 16, 2009 2:48 pm
Reputation: 0

Unread postAuthor: jackssmirkingrevenge » Wed May 06, 2009 10:10 pm

Looking good :) I like the magnet idea.

Just one thing, if you're not using an o-ring in the piston then the vent holes are unnecessary, air will still leak past the piston even if it's a very close fit.
  • 0

User avatar
jackssmirkingrevenge
Donating Member
Donating Member
 
Posts: 24225
Joined: Thu Mar 15, 2007 11:28 pm
Country: Holy See (Vatican City State) (va)
Reputation: 66

Unread postAuthor: LeMaudit » Wed May 06, 2009 10:15 pm

Really? Okay, it's easy to test without holes, then add them later than the other way around :-D

I figured the magnet will be easy to hold the ball bearing, but also to remove it (with a bigger magnet) so I can disarm the cartridges if necessary. With a rubber sleeve as planned first, the firing would have being mandatory.

Thanks again for all the advices.
  • 0

User avatar
LeMaudit
Donating Member
Donating Member
 
Posts: 665
Joined: Thu Apr 16, 2009 2:48 pm
Reputation: 0

Unread postAuthor: jackssmirkingrevenge » Wed May 06, 2009 10:28 pm

LeMaudit wrote:Really? Okay, it's easy to test without holes, then add them later than the other way around :-D


Trust me, you won't need them. Have a look at my prototype, you'll notice that the piston is a simple epoxy cylinder. Tight fit of course as it's cast in the actual tube it travels in, but it stil lets enough air to leak past to fill the chamber.
  • 0

User avatar
jackssmirkingrevenge
Donating Member
Donating Member
 
Posts: 24225
Joined: Thu Mar 15, 2007 11:28 pm
Country: Holy See (Vatican City State) (va)
Reputation: 66

Unread postAuthor: LeMaudit » Wed May 06, 2009 10:42 pm

I have no doubt the air would leak, but my first feeling would have being that it would not leak fast enough to create an equilibrium between the two sides of the piston in between two pumping. But I'm sure you're right of course ;-) I'm just discovering all this stuff.

Great fun this prototype of yours!!!
  • 0

User avatar
LeMaudit
Donating Member
Donating Member
 
Posts: 665
Joined: Thu Apr 16, 2009 2:48 pm
Reputation: 0

Return to Pneumatic Cannon Discussion

Who is online

Registered users: Bing [Bot], Google [Bot], Google Adsense [Bot], MSNbot Media, Yahoo [Bot]

Reputation System ©'