I has semiauto ;-)

[jackssmirkingrevenge]

so you're measuring your balls with a calliper... is that one of your many fetishes or something?

Just wanted to point out my balls were marginally bigger than yours

that's with a double stacked magazine ??

I'm thinking a 15-17mm tube as a mag

me thinks that an o-ring would work better... it's not a good idea to waste air... especially if you have such a small tank

I was thinking of including an o-ring too, but you need a detent to able to adjust.

Hmm that reminded of the pnuzi you should coat your gun in bondo and shape it and paint it.

Worky first, pretty later

Hit the paint section of your local hardware store and pick up some real Acetone to avoid these contaminants that will weaken the final product and slow drying.

Or find work in an industry that purchases Acetone in 1,000 litre IBCs

[POLAND_SPUD]

but you need a detent to able to adjust

uhmm... have a look at this but replace the burst disk with an o-ring... and voile you've got an adjustable o-ring

that's pretty much the same idea I use on a couple of home-made compression fittings

Just wanted to point out my balls were marginally bigger than yours

but my are more shiny

Oh and...are you sure about sticking to semi

who? me or JSR ?
I am building modular guns (thx to threaded fittings) so there is nothing that stops me from upgrading it to a full auto...
and I've think that the current version has proved that the design can handle full auto...
I could build a fully pneumatic fullauto version all I have to do is to buy one valve (pneumatically actuated 3/2 spool valve... it's discussed in more details here)

now that's you've mentioned sticking to something I realized that I don't know how to build the most imnportant part yet... a new T that will join the barrel, QEV and an air cylinder...

basically that's the only thing that I've got to build the rest stays the same or requires as much work as e.g. unscrewing 1/2" to 1/4" adapter and replacing it with a 1/2" - 1/8" one

[jackssmirkingrevenge]

Cast a small section of test barrel, fantastic tolerance not sure how durable it will be with high velocity steel rushing through it repeatedly but we'll see. If PVC can stand up to it I don't see why quality epoxy shouldn't.

have a look at this but replace the burst disk with an o-ring... and voile you've got an adjustable o-ring

that's pretty much the same idea I use on a couple of home-made compression fittings

I decided for a simpler option, two o-rings a couple of millimetres away from eachother as per diagram. Proper barrel curing as we speak, as is the paintball tank attachment. Now to sort out the magazine...

[POLAND_SPUD]

damn it... I am still waiting for the parts

I decided for a simpler option

Is it adjustable ?? I don't get it

[jackssmirkingrevenge]

Is it adjustable? I don't get it

That's how it's "simpler", it's the non-adjustable-fuck-it-I'll-alter-rate-of-fire-with-trigger-pressure approach hope to have it working brilliantly/proved useless within a few days.

[POLAND_SPUD]

in this way you can only adjust ROF but not power... I hope it will work but IMO it would be better if you could control both power and ROF at the same time...

ohh so you put them there when casting a barrel...??

uhmm....is it serviceable?
the design I proposed allows to replace an o-ring in a couple of seconds...

I mentioned that because you had some problems with non-serviceable designs in the past (and because others suspect that the o-rings will wear out sooner or later)

[jackssmirkingrevenge]

ohh so you put them there when casting a barrel...??

Yep.

uhmm....is it serviceable?
the design I proposed allows to replace an o-ring in a couple of seconds...

Nope.

I mentioned that because you had some problems with non-serviceable designs in the past (and because others suspect that the o-rings will wear out sooner or later)

Just a prototype, I'll kid myself into believing that if it works well I'll build a "proper" one

Actually, I might add a ball detent past the o-rings.

edit: here's progress so far, barrel is cast inside a section of (composite, of course ) fishing rod. What's left is to construct the magazine and detent setup and encase it in epoxy, hooked up to the socket, and attach the nipple to the pressure washer valve to enable the barrel/magazine setup to be removable in case I want to build other calibres

[jackssmirkingrevenge]

Sorry to have hijacked your thread with a build log but once the discussion started it seemed appropriate to continue posting here.

Here's the breech, before and after being unceremoniously entombed in an epoxy sarcophagus. I've gone for a simple vertical gravity fed magazine holding around 15 rounds, should be more than enough. Note the detent above the brass barrel mandrel, opposite which I've added a nut to make it more resistant to wear. I also squashed the magazine tube in a vice to give it a tapered shape towards the bottom which should make for reliable feeding. All it needs is another pouring of epoxy to reinforce and cap the magazine tube (which I deliberately factored in to give the breech more time to cure before I'm tempted to test it) and we'll see what it's capable of.

In many ways, it's a scaled up version of this project, which should obviously have much more power per shot (hence the relatively small magazine) and thanks to the blowgun being replaced by a pressure washer valve, I can use it to much higher pressures - unregged at 200 bar if I fancy

[POLAND_SPUD]

I don't mind it...
so it's just a prototype to prove the concept ??

and attach the nipple to the pressure washer valve to enable the barrel/magazine setup to be removable in case I want to build othe

Finally....


I always wondered what do you use to join and seal all the parts before pouring epoxy.. is it hot glue or cyanide glue ?

I already have the barrel so right now I am trying to build/mod the T... epoxy would help a lot but I hope I can get away with fittings and metal only...

ohh BTW I've just checked... threads on 88g CO2 cartridges are only slightly smaller than 3/8"

[jackssmirkingrevenge]

so it's just a prototype to prove the concept ??

Basically, though if it works well I might be persuaded to finish it properly, add an integral suppressor etc.

Finally....

Well, even if the 9mm setup doesn't work I'll still have a tank and trigger mechanism that can practically be used up to around 200 bar, and I don't plan on buying another pressure washer valve. It will make a good test rig

I always wondered what do you use to join and seal all the parts before pouring epoxy.. is it hot glue or cyanide glue?

It's araldite, dries relative quickly and is strong so there won't be any weak pockets once the epoxy around it dries. Also, when epoxy cures it's a fairly exothermic reaction especially in greater quantities, I suspect that hot glue would begin to fall apart.

[jackssmirkingrevenge]

Here's some tentative testing versus the usual 0.5mm aluminium plate, hooked up to a blowgun at 100 psi. Clearly the magazine feed isn't as reliable as I would have hoped (There would have been blasphemy accompanying the vigorous shaking had the camera not been rolling ) but the power's there, with the paintball tank I can take it to 450-850 psi so it should be even better. Who knows, perhaps it will also agitate the mag a bit and improve feeding.

[youtube][/youtube]

[youtube][/youtube]

I'll give it till tomorrow to make sure it's fully cured before taking it any higher though.

Here's the high pressure configuration:

[psycix]

And again he kills some smilies...
The sounds, LOLOL
SHHH -- rabmle rabmle -- SHHH --- ramble ramble -- LAZOR SOUND --- ramble -- SHHH
Especially the sound from the first vid at about 0:38 made me laugh. What the heck happened there?
"Floomp.... SHH-PFLOOOMP!"


Now onto serious prototype-related discussion:
Is the mag airtight? With my QEV+popoff I found that making a leak in the top of the mag allowed a small puff of air to ramble the BB's, improving feeding by a lot.

[jackssmirkingrevenge]

And again he kills some smilies...
The sounds, LOLOL
SHHH -- rabmle rabmle -- SHHH --- ramble ramble -- LAZOR SOUND --- ramble -- SHHH
Especially the sound from the first vid at about 0:38 made me laugh. What the heck happened there?
"Floomp.... SHH-PFLOOOMP!"

I know, I know... some kind of double feed

Now onto serious prototype-related discussion:
Is the mag airtight? With my QEV+popoff I found that making a leak in the top of the mag allowed a small puff of air to ramble the BB's, improving feeding by a lot.

Not really possible because the idea is basicallythis one so it cannot leak otherwise the pressure won't build up enough to fire.

[potatoflinger]

Why didn't you epoxy the aluminum plate to the box?

[psycix]

Not really possible because the idea is basically this one so it cannot leak otherwise the pressure won't build up enough to fire.

Pressure buildup? Hmm. You could always try, right?
Well anyway I think you'll have to use a tubemag.