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6mm single shot almost finished

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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6mm single shot almost finished

Unread postAuthor: andrew67 » Wed Mar 05, 2014 6:25 am

20mm t piece(home made QEV)
20mm/12mm epoxy piston
6mm/56cm barrel
modified air hose coupling(pilot valve)
20/100mm copper tube,housing the sprung piston for the trigger mechanism
86cm timber rifle stock
approx 400g benzomatic propane tank(air supply tank)

At an approximate 120-160psi it fires 6mm plastic pellets consistently accurate over an estimated 10meters,using 6mm lead pellets approximately 20meters accurately but with more pressure a gauge and better ammo I'd expect a much better result.

A few days after writing this I've tested at approx 170/180 psi,it seems at higher psi (above 140) performance drops dramatically ,so I'm unsure of this being fixed so that higher pressures can be used or it's just the limits of the rifle?
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In the cocked position
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In the fired position,as it's fired there's two O-rings to keep the loading chamber sealed from escaping air.
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Re: 6mm single shot almost finished

Unread postAuthor: jackssmirkingrevenge » Wed Mar 05, 2014 7:29 am

Not bad!

Higher pressure should mean more power...

How solid is your piston? what does your sealing face look like, how is it attached to the piston?

Also, I didn't get exactly how you are piloting the valve?
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Re: 6mm single shot almost finished

Unread postAuthor: andrew67 » Wed Mar 05, 2014 6:17 pm

Thanks!
I'll take photos of the first firing mechanism I made (same concept)
The piston is epoxy with thin rubber almost the same as bike tube super glued on!
It seems to lack power as pressure gets higher almost like the pressure is holding the piston against the barrel I'm not sure?do you think it's possible?
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Re: 6mm single shot almost finished

Unread postAuthor: andrew67 » Thu Mar 06, 2014 2:40 am

This is the inside of the pilot mechanism,it's the first one I used but it was sloppy and weak so kept the same concept but used heavier material,reasonably simple drag the copper piston back and slide the lever over in the slot you can see in the half inch copper tube (as the mechanism fits inside that)
To fire,flick the the lever out of the slot the piston then slams the male air line fitting into the female fitting releasing enough air to fire the QEV.
On the finished rifle there is no slot to slide the lever into,instead there is a small hole for a sprung screw for the piston to catch on when pulled back the screw is attached to a lever so when the lever is pushed the screw comes out of the hole and releases the piston.
The lock and release mechanism is inside the aluminium piece that's hose clamped to the pilot mechanism (first photo)
Hope you understood all that?
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Re: 6mm single shot almost finished

Unread postAuthor: jackssmirkingrevenge » Sat Mar 08, 2014 10:06 am

andrew67 wrote:The piston is epoxy with thin rubber almost the same as bike tube super glued on!


It's better to hold it with a bolt and washer.

It seems to lack power as pressure gets higher almost like the pressure is holding the piston against the barrel I'm not sure?do you think it's possible?


Is the piston in the tee or in the copper tube? Copper pipe is usually not perfectly round, it could be that your pilot valve has low flow compared to the air which escapes around the piston.
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Re: 6mm single shot almost finished

Unread postAuthor: andrew67 » Mon Mar 10, 2014 4:17 am

Seems to be the pilot valve not releasing enough air,it was just coincidence it started doing this when I tried more pressure,I'm in the process of adjusting it so I expect it will have better performance
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Re: 6mm single shot almost finished

Unread postAuthor: andrew67 » Fri Mar 21, 2014 8:24 am

After a bit more testing I found that the epoxy piston had deformed slightly ,now that is fixed its power has increased with the extra pressure.
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Re: 6mm single shot almost finished

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Re: 6mm single shot almost finished

Unread postAuthor: jackssmirkingrevenge » Sat Mar 22, 2014 4:58 am

so... let's see it in action!
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