Back to PCP !

[LeMaudit]

Hi guys,

Following my Kick’n’Blow concept and after computing a few values for spring forces and playing more with GGDT, I finally concluded that a spring will never be able to reach some interesting power with the short overall length I seek for my project. So I’m back to the drawing board, with my first idea as a PCP six-shooter (or five !)

I have learned a bit about the existing chamber concepts, thanks to the great Wiki.
My idea is finally a mix with an oversized Brocock cartridge, a sort of barrel seal but with direct flow and no vent hole so I guess it is more like a Chamber seal in term of efficiency. I would like to use the Schrader valve both as an intake and as a trigger.

I designed it to be easily machinable, there’s no real difficult piece there. And I guess it can be easily oversize to fire some spuds so you may find it interesting enough.

Also, I have difficulties to estimate GGDT results for potential damages
I intend to fill the chambers at 135psi, which is the power my workshop compressor provides. What do you thing of those results, a 3/8 steel ball bearing at 228 ft/s and with a kinetic energy of 6.4 feet-pound. Is it serious, average or weak?

Of course, the same with a 3 or 4 foot length barrel become even more powerful, and thinking about it, it would not be the first gun that can be transform to a rifle

[spudtyrrant]

first comment yay, nice design its kinda like a mini toolie piston you could attach a mini qev popoff and make it full auto, again nice design, when i first saw the name it sounded like something bad but its actually something good

[jackssmirkingrevenge]

Reminds me of an idea I once had

Looks good, but you really should consider ashock pump to go to higher pressures. 6 ft/lbs is the legal limit for air pistols in the UK, not bad in terms of power but you can do better

[LeMaudit]

You sure had the same idea... or is it me that had the same... I didn't look, I swear ! But very close indeed...
Did you build it?

I'm not familiar with those items: Shock pump. I read a bit about them through the forum. I am guessing they are capable of high pressure, a tiny amount at a time. Right? How much time do you think would be needed to go from 135 to say, 300psi on my 1.5 in3 cartridge?

300 psi would double the muzzle energy, and increase by 50% the velocity. Just like having a 3 foot long barrel at 135psi

And 300psi + 3 foot barrel is really nasty... 30 ft*lb and 490 ft/s

I really have no clear idea about what pressure my cartridge could take. The good thing is that it I want to do more, I'll just have to pump. I'll make sure to oversize the attachments, just to be safe. How much do you think it could take, reasonably? I intend to attach the brass to the aluminium cylinder with several steel spring pins, and a 1" diameter O-ring to seal it.

[jackssmirkingrevenge]

I'm not familiar with those items: Shock pump. I read a bit about them through the forum. I am guessing they are capable of high pressure, a tiny amount at a time. Right? How much time do you think would be needed to go from 135 to say, 300psi on my 1.5 in3 cartridge?

Have a look here (second one on the list is brilliant ), cheap and for small chambers it doesn't take long to get to high pressure.

300 psi would double the muzzle energy, and increase by 50% the velocity. Just like having a 3 foot long barrel at 135psi

For smaller calibres, higher pressures really make a difference, especially if you're limited in barrel length and chamber size.

I really have no clear idea about what pressure my cartridge could take. The good thing is that it I want to do more, I'll just have to pump. I'll make sure to oversize the attachments, just to be safe. How much do you think it could take, reasonably? I intend to attach the brass to the aluminium cylinder with several steel pins, and a 1" diameter O-ring to seal it.

If it's an all metal cartridge would say it should take 300 psi easily, even 400 if the wall thickness of the chamber is big enough. In my cartridges I was using a PVC body (with a 3.5mm wall thickness) and they take 400 psi without problems.

One word of warning which I found out with my prototypes, with pressure the cartridge tends to expand slightly, so if it's a tight fit in your breech when empty it might get stuck when under pressure.

[LeMaudit]

Thanks again for the link and advices. I do intend to make the cartridges removable, first to have at hand several cartridges on a belt maybe (hmmm... why to I think about Rambo suddenly) and also because I intend to use the gaz-ejection from the valve to turn the barrel for the next shot. So the valve will be internal. But that's another story

[jackssmirkingrevenge]

I intend to use the gaz-ejection from the valve to turn the barrel for the next shot.

Like the Webley-Fosberry?

[LeMaudit]

Didn't know that ! I have to check for this gun, and possibly blue prints
Damn... so many things to learn

[Gippeto]

LeMaudit, it's an interesting proposal, and definitely do-able.

I will tell you from experience though, that the o-ring on the sealing plug will depart down the barrel with the first shot.

Consider machining a teflon or delrin seal, and attaching it with a small counter sunk screw.

[LeMaudit]

I will tell you from experience though, that the o-ring on the sealing plug will depart down the barrel with the first shot. Sad

Consider machining a teflon or delrin seal, and attaching it with a small counter sunk screw.
_

You think so? hmmm... I think you're right. I have very little experience with O-rings. Well, machining a washer seal is not a big deal. Thanks I'll keep that in mind.

[jackssmirkingrevenge]

Didn't know that ! I have to check for this gun, and possibly blue prints

As far as I know it works like the Mateba, the recoil moves back the upper assembly and through groves in the magazine it recocks the action. I doubt a PCP will generate enough recoil to accomplish this however, I think a simple double action like most revolvers is a better idea.

[i-will]

i'm planning on building that piston for my bolt action cannon but with a hammer valve.

[Ragnarok]

As far as I know it works like the Mateba.

Not quite the same. The ramping is different between the two, but they do work in largely the same manner.
And evidently, the maker of that video has got single and double action the wrong way around.

But I quite agree - recoil based reloading mechanisms are not an area at which spudguns can excel.

[jackssmirkingrevenge]

And evidently, the maker of that video has got single and double action the wrong way around.

Italians eh

But I quite agree - recoil based reloading mechanisms are not an area at which spudguns can excel

It depends, large combustions for example generate more than enough recoil to eject a cartridge

[LeMaudit]

As far as I know it works like the Mateba,

Fascinating! Thanks for letting me learn about those. I love those mechanical concepts...


Well, my idea was not to have a full cocking only with the air, I'm aware it would certainly not be enough. I was planning more to have a mechanical one like a revolver, but after the firing just use the small quantity but highly compressed air that came out when I press the trigger, to store it in an additional chamber, and use it somehow when te trigger is released to turn the barrel for the next shot. If it is mounted on a ball bearing it would not need much force.

But this is clear as mud in my mind for now and I need to think more about it. This will be the opportunity for some additional drawing I'm betting I need to have the pressure in that chamber low enough to let the firing be done, so this means a chamber big enough, and maybe this will not then be enough at all to activate anything.

It sure would be nice not to have the air expulsed at the moment the firing is done, to keep some accuracy in the aiming. I'm guessing the pulse of air would deviate the gun somehow. So expulsing it to the atmosphere at the trigger release is anyway a good thing IMO.