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I too has semi-auto

Built a pneumatic cannon? 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: Gun Freak » Sat May 22, 2010 9:11 am

White lithium grease.
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Unread postAuthor: Lockednloaded » Sat May 22, 2010 12:58 pm

i have some teflon paste, would that work?
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Unread postAuthor: Gun Freak » Sat May 22, 2010 1:18 pm

I have no idea, I just always hear people talking about using white lithium grease.
Try it. If it doesn't work, wipe it off and get some grease :)
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Unread postAuthor: django » Sun May 23, 2010 1:25 am

Im trying to get one of those Air Cylinders now,Ive emailed that seller for a shipping cost to Australia but if its too$$$ I wont proceed :roll:

One thing I dont understand is: doesn't the qev fire the burst of air before that cylinder can activate the arm out?,because of where the QEV is I mean, I would have thought that the air would just fire out before that cylinder arm can push the BB forwards?.........
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Unread postAuthor: psycix » Sun May 23, 2010 5:19 am

Nice job. How about changing the bolt head? The tube with holes drilled in it is kinda flow-restrictive and I recommend you switch to a pin.
The pin pushes the ammo past the QEV port, and the air can flow freely around the pin.

EDIT:
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Unread postAuthor: jor2daje » Sun May 23, 2010 11:36 am

I was considering a pin when a made it but I think if i start firing to rapidly the pin may get under the bbs and just push them back up into the mag instead of loading it forward. But your definetly right about the flow restriicition.

@django the cylinder actuates really quickly, Ive never had it fire berfore the cylinder has fully opened.
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Unread postAuthor: POLAND_SPUD » Sun May 23, 2010 5:12 pm

if I start firing to rapidly the pin may get under the bbs
I don't think it can be a problem... I mean, it is not that you get this problem with a pin but not with a solid bolt...

in both cases it can happen... though it is very unlikely - the bolt would have to retract almost completely and then instantly advance forward
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Unread postAuthor: jackssmirkingrevenge » Wed May 26, 2010 12:23 am

I'm absent for a couple of weeks and semi-autos start springing up all over the place :roll: nice one!
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Unread postAuthor: django » Wed May 26, 2010 4:37 am

Guys, I got no response from the Ebay seller of those Air Cylinders so sadly looks like I wont be making a similar gun :roll: .Auction even says International buyers email for post costs!?.

EDIT: theres a place near my work that sell Clippard Air Cylinders, I have a big clippard catalog from them( I forgot about it!). Now Im going to make the gun small as possible ,I see they have Air Cylinders ( single acting Micro Cylinders)with the bore sizes at
8mm!
12mm
16mm
20mm
25mm
all with bore strokes available in 10,25,40,50,80+100mm

I'll be running the MVOV-3 poppet valve as pilot and a 1/4" qev, what size Air Cylinder do you guys recomend? I mean is the 8mm bore size too small?.I just dont want to buy one then find out the gun wont feed properly due to the air cylinder not actuating quicker than the Qev etc
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Unread postAuthor: POLAND_SPUD » Wed May 26, 2010 7:06 am

@django
IIRC those small bore air cylinders are rated lower than standard ones... I've been thinking whether it is possible to strenghten them by threading them all the way into a coupler (the ones I've seen are all threaded on the outside so it might work)

MVOV-3
you meant MJVO-3, right ?

If you already have some experience with semis you might as well build something new...
for example a gun with an under barrel magazine and a loading mech similar to the one used on giardoni air rifles (I hope I spelt it correctly)
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Unread postAuthor: al-xg » Wed May 26, 2010 12:19 pm

to achieve fully automatic fire you need either:
1. solenoid valve and time relay/555timer
2. time delay valve


Or add a switch that brakes the circuit when the air ram leaves the forward position. That also gives a synchronised system where the valve only fires when the bolt successfully moves forward.
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Unread postAuthor: DinerKid » Wed May 26, 2010 2:09 pm

This is a really cool design. I do have one question though. What stops the ammo from falling into the second T when the piston pushes it forward?

~DK
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Unread postAuthor: POLAND_SPUD » Wed May 26, 2010 2:31 pm

you don't need anything... on the semiauto MKIII that port is as large as any other port...

the rod moves so fast that the ball can't fall and the rod in its forward most position prevents the ball from falling down
the ball falls in only if the air cylinder is not threaded in all the way in

yeah, it is that simple
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Unread postAuthor: django » Thu May 27, 2010 7:22 am

POLAND_SPUD wrote:@django
IIRC those small bore air cylinders are rated lower than standard ones... I've been thinking whether it is possible to strenghten them by threading them all the way into a coupler (the ones I've seen are all threaded on the outside so it might work)

MVOV-3
you meant MJVO-3, right ?

If you already have some experience with semis you might as well build something new...
for example a gun with an under barrel magazine and a loading mech similar to the one used on giardoni air rifles (I hope I spelt it correctly)



Ooops!,I meant MJVO-3 Poppet Valve= looking at the specs on the Clippard Micro Air Cylinders they are rated to 17 bar (246 psi) would be nice to run more but It'll do me :)
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Unread postAuthor: POLAND_SPUD » Thu May 27, 2010 7:50 am

yeah sorry I thought that I've seen these in clippard catalogue

17 bar is a lot (usually stuff form other companies is rated to 10bar max)


MJVO-3 valve is pretty much the best valve you can get... I've compared hundreds of data sheets and most 1/8" valves that I could find cost about 30-50 euro excluding shipping and taxes but clippard sells MJVO-3 for about 12$ not including taxes etc.

also check their QEVs - you can order them with male threads... it might not seems as much but it helps to reduce number of fittings and dead space to minimum
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