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Full auto prototype

This area is for the discussion of BB or airsoft sub machine guns, and or other small arms such as pellets.
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Unread postAuthor: POLAND_SPUD » Thu Aug 13, 2009 10:52 am

I can't imagine a high pressure automatic would be easy to get away with in town
I live 1 km out of town and I have 1ha of my own land.. the closest neighbour lives ~120 meters away...

after a few shooting sessions with my semi auto project my neighbours started to ask a lot of questions about 'strange noises' coming from my backyard

apparently you can get away with single shots because they seem to come out of nowhere and are unexpected so it's harder to tell from where they come from... plus there are lots of things that sound similar to a gun shot: fire crackers, commercial air guns or some tools



If the calibre of des-2 is small enough you could build a silencer... but you've probably though about that already?
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Unread postAuthor: jimmy101 » Thu Aug 13, 2009 1:16 pm

inonickname wrote:I used HSS precision twist bits. They are brand new, and razor sharp. I hate to use a machinists vice bolted down, and everything clamped in tightly, along with lots of lubricant. I cracked several, but those were before I set up the machinists vice on the drill press.

I tested it, but the cycling was unreliable and much too fast. I experimented with a stiffer spring, and cycling became extremely unreliable. I may experiment more, but in all honesty a QEV and popoff is a much simpler, reliable and powerful method.

I'm surprised standard HSS bits worked. Usually they have way to much rake and grab and lift the material. It's pretty easy to regrind a standard bit to get it to work much better with plastics.

I wonder if moving the vent hole and/or resizing it would be a good way to tune the performance?
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Unread postAuthor: jackssmirkingrevenge » Thu Aug 13, 2009 1:54 pm

POLAND_SPUD wrote:after a few shooting sessions with my semi auto project my neighbours started to ask a lot of questions about 'strange noises' coming from my backyard


Agreed, one off noises could be dismissed as anything but the hammering of something like my pop-off valves, especially the HPA ones, is a little harder to explain away as being innocuous.
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Unread postAuthor: kozak6 » Mon Aug 17, 2009 11:34 pm

Do you think a heavier piston and a longer cylinder tube with a differently placed vent hole could slow down the rate of fire down to something more practical?

What if instead of venting through a plain hole, it vented through some sort of automatically resetting pop safety valve? If I'm thinking about this correctly, and the unit were sufficiently airtight, the piston wouldn't be able to move until enough pressure built up to pop the valve open. This would allow some pressure to build up for more power, and should slow the rate of fire down.

I wonder if more complexity is what this design needs, though.

Have you considered building an airsoft style BV unit? Conceptually, it's a little simpler, but building it might be about comparable to this one.
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Unread postAuthor: jackssmirkingrevenge » Tue Aug 18, 2009 12:45 am

kozak6 wrote:Have you considered building an airsoft style BV unit? Conceptually, it's a little simpler, but building it might be about comparable to this one.


You've mentioned this before but I don't think anyone here ever actually made one.

Image

System is pressurized. Subchamber/barrel assembly is in the normal, unpressurized full back position.

Trigger is pulled, opening valve in gas block

Gas passes trigger valve, entering the magazine's rear port.

Gas blows BB into subchamber, pressing the BB against O-ring and closing the pressure circuit

Pressure builds behind BB, forcing barrel and subchamber assembly forward against barrel spring until forward travel stops. Pressure behind BB increases further. In moving forward, the subchamber blocks any further BBs in the magazine from loading. Its sloped rear wall pushes the extra BBs back into the magazine.

BB compresses O-ring sufficiently to pass through, releasing pressure in the subchamber and allowing barrel spring to push barrel and bolt assembly back, opening chamber for another BB. At this time the system is still pressurized, with gas flowing out through bolt assembly and out barrel.

With the subchamber/barrel assembly in the full back position, gas continues flowing through the magazine, starting the cycle again from step 4. This continues until trigger is released, closing the valve and stopping the gas flow.


It is a comparatively simple design and succesfully marries a reloading and valve mechanism but I bet you'd need a lot of tweaking with spring strength and o-ring tightness to get it right.
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Unread postAuthor: SEAKING9006 » Fri Aug 21, 2009 9:45 am

Eh. It's these kind of problems that caused me to abandon trying to go for full auto based on a valve design, rather than a bolt. The most promising concepts I have come up with would be a double-action hammer hitting a hammer valve for semi auto, and a blowback bolt (in an open-bolt design) that holds down a reed valve in the charged position. The reed pilot is something I came up with just recently. The idea is somewhat similar to a fixed ejector in that it is embedded in the wall of the bolt carridge and pivots to go flush with the wall when pressed on by the bolt. This is what pilots the QEV, rather than a hammer valve. As the bolt flies forward off of it, the pressure pushes it up and pilots the QEV. There is another pilot valve at the front of the bolt carridge (either reed or another type) that closes the valve that dumps air into the primary chamber, fed by a CO2 can. As it recoils back, it opens this valve allowing it to fill the chamber again. Combine this with a rotating bolt, and you have something that will get you into ANY college. (I'm trying for SMU-Lyle.) Obviously complex and hard to build, but it ought to work.
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Unread postAuthor: twizi » Fri Aug 21, 2009 11:16 am

what about a hose leading to a ball valve that has a barrel attached so the hose act like a barrel like jsr prototype but has a backpack with 4inch pvc tank ful of bb then a air hose goin right next to the inlete to the hose to the ballvalve and barrel so it act like a cloud or a vortex but with a 8 foot barrel at the presure it would be perfect for airsoft like a flame thrower prototype
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Unread postAuthor: joepage2008x2 » Sat Aug 22, 2009 3:34 pm

Someone on the first page mentioned why make a fully automatic bb gun, why not use a cloud or vortex. Answer - a cloud may take a lot of time to reload as with a vortex, with this way you can add a magazine.

Im in the process of making a bb gun. I thought about a blow - back design then a blow-forward design. The problem is that a lot of the designs that are fully automatic or use the blow forward/back are pretty weak. So after a few hours on my lathe i have built part of my gun, the hardest part - the blow-forward part. I will be making a semi-automatic shotgun because my gun loads 3bb`s at a time - this wil be adjustable 1 to 3. Im hoping for around 600fps or more. Its a lot bigger than it should be but with the way that im making it means that i can tweak it. (dont want to waste air if i take it to a game).

My only problem is that all of my pumps have broke, i cannot find a fridge thats been dumped and one of the belts in my lathe has snapped :(
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Unread postAuthor: twizi » Sun Aug 23, 2009 6:40 pm

u can have tubes or pod like a paintball gun cloud take two second to reload as quick as a mag/clip
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