Posted: 08/31/2010 14:56 PM Post subject: Another hybrid cartridge prototype
Master Sergeant
Joined: 23 Nov 2008 Posts: 171 4.29 Spud Bux
here's another hybrid cartrige concept, based on JSR's work but a bit different:
The top part is the cartridge, just a piece of 28mm copper with a schrader and a 'hook' epoxied into one end. The hook forms one side of the spark gap and is also an attachment point for the breakable link.
The bottom half is the projectile which is a 1/2" iron nipple glued into a section of aluminium pipe, there is an o-ring on the back and a rod through the middle. A loop of cord or wire (the breakable link) is tied around this rod, the two halves are fitted together and a twist secures the breakable link under the hook.
the following vid is a pneumatic test using some quite strong cord as a breakable link, it proved to be too strong and I had to twist it around before it blew at about 150-200psi.
despite only having about 2" of barrell I managed to stick the projectile into the concrete wall
unfortunately the recoiling cartridge ended up on the floor with a dent in it, copper in not ideal for this I will use a thicker aluminium tube for the next one. I'm also going to experiment with some different materials for the breakable link before moving onto a 5x mix test.
any comments or suggestions welcome
The projectile is retained by a chord (high tensile fishing nylon?) and is fired by a hot wire cutting it thus releasing the projectile. A perfectly airtight projectile would have too much drag, so the best idea would be to have an O-ring at the breech so it is only 100% airtight when it needs to be.
It was just a theory though, it's great to see it being actually implemented spudamine, what are you doing for fuelling? In spite of some success with smaller chambers on my part, fuelling is far from reliable with the methods I have tried to far.
I had actually proposed a similar idea on spudtech as a pneumatic "valveless" concept
I thought somebody would've probably come up witth something along these lines before, why am I not surprised it was you
I was also thinking of fishing line, it even comes with different breaking strain ratings. I'm a bit worried about the friction of the o-ring in the barrel but it seems to work for those sureshot compound rounds, hopefully the added friction will just cancel out the removal of blowby.
Damn I'm out of schraders, I've even nicked one from my spare inner tube, sod's law I get a puncture tomorrow.
EDIT:
as for the metering, first stop will be having a go with the manometric system from my old hybrid. If that fails then I'll need to have a good think about it
Joined: 15 Mar 2007 Posts: 18061 32519.23 Spud Bux
spudamine wrote:
I thought somebody would've probably come up witth something along these lines before, why am I not surprised it was you
Well you thought of it independently and actually built it, so credit to you
Quote:
as for the metering, first stop will be having a go with the manometric system from my old hybrid. If that fails then I'll need to have a good think about it
the object of my invention is to prevent the projectile from being puffed partly or entirely out of the gun before the propelling force is sufficiently developed
I guess faster burning propellants finished this one off.
I've shelved this idea for now, far too fiddly for mass production of cartridges and it's too bloody cold to make anything at the moment anyway.
Joined: 15 Mar 2007 Posts: 18061 32519.23 Spud Bux
spudamine wrote:
I guess faster burning propellants finished this one off.
Not really, the PAW 600 uses a similar system where the projectile is released when a retaining rod fails when a certain pressure is reached, and in some ways the basic design of most western 40mm grenade cartridges relies on the same principle.
You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum You cannot attach files in this forum You can download files in this forum
spudamine, what are you doing for fuelling? In spite of some success with smaller chambers on my part, fuelling is far from reliable with the methods I have tried to far.
