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9mm SMG project + other HPA BBMG experimentation

Built a BB Machine Gun? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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Unread postAuthor: POLAND_SPUD » Mon Oct 12, 2009 7:57 pm

so have you abandoned the idea ??

you might add something that would prevent double feds... that's the first thing that came to my mind...
the rod of the air cylinder would keep the second bb from being sucked into the barrel right after the first one fired
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Unread postAuthor: jackssmirkingrevenge » Tue Oct 13, 2009 12:32 am

That goes against my quest for simplicity, but the "pop-off projectile" idea is one of the best concepts out there since someone first shook a bottle of champagne, it's too good to give up on.

For the moment I think I'm going back to this idea.

The vortex block BBMG is a proven concept, and I believe that by adding a restriction it would work for the reasons outlined in the thread:

Objections:

1) You need airflow through the chamber to suck the pellets into the barrel

2) You won't get the airflow until a pellet stops blocking the barrel by overcoming the sprung ball.

Could mean less balls in the barrel at once but also less reliability in feeding.


Reasoning:

These were my initial thoughts but on reflection it doesn't seem contradictory. You get BBs agitated until one gets sucked into the barrel and flow stops, it eventually pops at which point you get airflow again and the cycle continues. Considering the rate of fire of standard BBMGs it shouldn't be a long interval between a BB firing and another getting sucked in.


The fact that the BBs aren't directly in line with the breech and need agitation before reaching it should technically remove the double feed issue.

Brian the brain wrote:I understand.... :D


Of course you do, now we drink from the same cup ;)

:shock:

Two spudders one cup, ewwwwwww! :?
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Unread postAuthor: psycix » Tue Oct 13, 2009 5:11 am

The whole idea of dakka-dakka was to maximise individual shot power to compensate for the fact that I was stuck with compressor pressures - but now that I have HPA on tap, I want to milk it for all its worth

My suggestion:
"maximise individual shot power + HPA on tap"
:wink:
DAKA-DAKA-DAKA instead of daka-daka-daka or BRAAAAP.

I could machine a high pressure rattlesnake... but I'm not sure about its ability to maximize individual shot power. I believe QEV+popoff has more power (and, a lower efficiency).


Two spudders, one cup of epoxy. :\
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Unread postAuthor: jackssmirkingrevenge » Tue Oct 13, 2009 7:12 am

psycix wrote:My suggestion:
"maximise individual shot power + HPA on tap"
:wink:
DAKA-DAKA-DAKA instead of daka-daka-daka or BRAAAAP.

I could machine a high pressure rattlesnake... but I'm not sure about its ability to maximize individual shot power. I believe QEV+popoff has more power (and, a lower efficiency).


With my HPA Rattlesnake the power was certainly there, but yes, probably the QEV+popoff is more powerful - however the point I was trying to make here is that with a detent style setup, you have maximum power (because there is no valve opening time, you get full flow immediately) and efficiency (because no air is wasted on pilots and pistons etc.)

The challenge seems to be twofold, getting the projectile to "pop" at or almost at the maximum pressure your tank is putting out, and reliable feeding.

Two spudders, one cup of epoxy.


Oh dear.

Freshly mixed or cured :roll: :D
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Unread postAuthor: POLAND_SPUD » Tue Oct 13, 2009 7:30 am

is it really that complicated ?? I don't think so all you need is a small air cylinder and a fitting to screw it in...

Two spudders one cup

and I thought that foot fetish was weird :shock:
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Unread postAuthor: psycix » Tue Oct 13, 2009 10:51 am

I'm going to build a final popoff prototype first, and after that I might look into a rattlesnake.

jackssmirkingrevenge wrote:Oh dear.

Freshly mixed or cured :roll: :D

Half-cured. A little sluggish. Gives a funny feeling when between your toes.
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Unread postAuthor: Brian the brain » Tue Oct 13, 2009 11:41 am

That should warm me up nicely inside...
But helas,

I don't wear a cup... :roll:

how about a pop-off like piston that pops out of the way at a certain pressure??
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Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

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Unread postAuthor: jackssmirkingrevenge » Tue Oct 13, 2009 12:21 pm

Brian the brain wrote:[size=9]That should warm me up nicely inside...


... being a significantly exothermic reaction and all that :roll: but aaaaaanyway...

how about a pop-off like piston that pops out of the way at a certain pressure??


Why the complication when you can have the projectile popping off at a certain pressure? No restrictions, no dead space, no pilot volume, this seems to be the best solution.
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Unread postAuthor: psycix » Tue Oct 13, 2009 12:50 pm

Because that calls for a complicated magazine and loading system that is hard to build jam-proof or doublefeed-proof.
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Unread postAuthor: Brian the brain » Tue Oct 13, 2009 2:15 pm

This could go on for ever... :cry:


Be like Nike and just do it!
:D
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Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

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Unread postAuthor: jackssmirkingrevenge » Tue Oct 13, 2009 2:18 pm

Making a wierd untested vertical vortex block as we speak :D

edit: didn't put a detent on it this time, just a silicone rubber seal, and so far at 450 psi it's too tight for the BBs to be popped out, we'll see what upping the pressure does tomorrow.
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Unread postAuthor: jackssmirkingrevenge » Tue Oct 20, 2009 2:24 am

jackssmirkingrevenge wrote:we'll see what upping the pressure does tomorrow.


Well, we sure saw what it did :roll:

In this regard, my next development is built in a stainless tee which is highly unlikely to fail in the same manner.

The breech is currenly curing, as per the diagram below. There's no mechanical detent as before, just a silicone seal, and in order to avoid jams I've added a "coaxial block" so to speak, together with a suitable angled air inlet to promote agitation. We'll see how well it actually works.
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Unread postAuthor: JDP12 » Tue Oct 20, 2009 9:37 am

wow looking very sweet JSR
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Unread postAuthor: jackssmirkingrevenge » Tue Oct 20, 2009 10:39 am

I tried it out earlier hooked up to my compressor, but 110 psi isn't enough to push a BB through the seal. I'm hoping the 20 or so pounds of force on the projectiles provided by the air with the paintball tank at 850 psi will be sufficient to pop it out like a champagne cork :D unless it blows up, we'll see :roll: :D

edit: me and my lack of patience, I managed to blow the top out of this one too :roll:

Clearly the silicone seal is a bit too much, I think an adjustable ball detent is ultimately a better idea at these pressures. Back to the workbench...
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Unread postAuthor: POLAND_SPUD » Tue Oct 20, 2009 1:34 pm

hmmm
you know what... since you already use fittings you might as well use THREADED fittings

it would make some sense since the top of it was for loading ammo, right ??
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