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adjustable rate of fire for BBMGs?

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: Carlman » Wed Jan 30, 2008 3:58 am

@SPG this was done in someones 12g c02 bb pistol, except they didnt use wire to change the ID, it gave a pop - pop - pop ROf instead of brrrrrrr
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Unread postAuthor: jackssmirkingrevenge » Wed Jan 30, 2008 4:48 am

SPG, that would probably provide a better seal. Still, I think I'd be more inclided to use the detent system, as it would be incrementally adjustable.
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Unread postAuthor: SPG » Wed Jan 30, 2008 6:12 am

Jack, this was something I came up with a long time ago for a BB Hybrid idea (the same one I'm still thinking about in fact).

In theory it should be as infinitely adjustable as your system, what I'd come up with was using a thin steel cable (think bicycle gear cable). You'd fix one end, then make a complete loop round the tubing, and bring the other end out to a screw in adjuster (again think the adjusters on bicycle brake and gear levers). Then you could adjust it simply with a turn of the screw, just like yours.

Another alternative would be to have a barrel inner and outer tube, (like an airsoft rifle) and have one screw inside the other. Then put your tubing between two parts of the inner barrel (a bit like an O-ring). Simply screwing the inner barrel in or out would give you an adjustable air-tight detent. Obviously then you could have a low-rate, high-power shot, or a high-rate, low power shot.
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Unread postAuthor: jackssmirkingrevenge » Wed Jan 30, 2008 6:36 am

Another alternative would be to have a barrel inner and outer tube, (like an airsoft rifle) and have one screw inside the other. Then put your tubing between two parts of the inner barrel (a bit like an O-ring). Simply screwing the inner barrel in or out would give you an adjustable air-tight detent. Obviously then you could have a low-rate, high-power shot, or a high-rate, low power shot.


I was actually contemplating this compromise solution.

I realised that with all this talk of reciprocating bolts and pop-off pistons, things have veered considerable from the original "keep it simple" premise - the more complex things get, the more there is to go wrong, and I'm not too keen on that.

The disadvantage of this idea is that you're limited to hard spherical projectiles, which for all practical purposes means airsoft or steel BBs, and pissibly marbles.
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Unread postAuthor: SPG » Wed Jan 30, 2008 6:47 am

Indeed, and I know that your endgame is a a semi/fully automatic pellet gun.

And that's going to be hard to build.
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Unread postAuthor: jackssmirkingrevenge » Wed Jan 30, 2008 7:09 am

jackssmirkingrevenge wrote:which for all practical purposes means airsoft or steel BBs, and pissibly marbles.


Oh dear got, I just realised I sound like Officer Crabtree, the "polocemen" from 'allo allo!

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gid moaning...
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Unread postAuthor: Ragnarok » Wed Jan 30, 2008 7:13 am

I was considering making that joke... but did decide against it - until you brought it up.
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Unread postAuthor: jimmy101 » Wed Jan 30, 2008 12:01 pm

SPG wrote:Ah-hah, here's just a thought for one and all. Places like aero-modelling shops sell silicon rubber tubing in a variety of small diameters including one with a 6mm ID.

Now imagine you take a short bit of this, push the barrel end in part way and push the whole thing onto the chamber outlet, LEAVVING a small gap between the two rigid tubes. Now you could do something as simple as wind a piece of wire round this and twist it to constrict the tube. And voila very simple adjustable system, completely air tight and providing a good BB to tubing seal.

Oh and it's cheap stuff but you usually have o by it by the metre/yard, so when one bit wears out you just fit another bit.

Ya mean kind of like the rigfht hand drawing in the top row of;
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Jack-
Good point. In the designs I was contemplating, I thought that perhaps you could take the right hand drawing in the top row of the figure above and put the short length of rubber tubing inside a compression T. You could then partially pressurize the T and control how much pressure has to build up behind the BB before it is forced through the tubing.
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Unread postAuthor: Anokiernan » Thu Jan 31, 2008 12:13 am

If you go with that spring loaded ball detent idea, you'll more than likely run into a problem with the spring floating. At the high rates of fire these guns are capable of, after the first few "controlled shots" the spring won't have enough time to recover fully and the design will collapse from there...
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Unread postAuthor: jackssmirkingrevenge » Thu Jan 31, 2008 2:29 am

It depends on the stiffness of the spring as well as the travel, the detent only has to be a tiny distance into the barrel to stop a BB so I was thinking in practice this wouldn't be an issue.
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Unread postAuthor: jimmy101 » Thu Jan 31, 2008 11:52 am

jackssmirkingrevenge wrote:It depends on the stiffness of the spring as well as the travel, the detent only has to be a tiny distance into the barrel to stop a BB so I was thinking in practice this wouldn't be an issue.

Multiple BBs per cycle may still be a problem though. In my very crude single shot setup (based on RC warship single shot guns) the piston, even when driven by the air supply, can't move fast enough to limit the BBs/cycle to one.

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A better solution might be to just not have more than one BB at the breech at a time. A cloud or vortex design should do this automatically.
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Unread postAuthor: jackssmirkingrevenge » Fri Feb 01, 2008 3:22 am

You could then partially pressurize the T and control how much pressure has to build up behind the BB before it is forced through the tubing.


Ingenious, you get a good seal and infinitely adjustable pressure.

How about some sort of air driven rotor?
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Unread postAuthor: c0rpse » Tue Apr 01, 2008 4:36 pm

Did anyone ever try this idea with the spring loaded detents? Would it work better with a cloud or vortex?
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Unread postAuthor: Lentamentalisk » Tue Apr 01, 2008 6:34 pm

What I dont entirely get is how this works with a vortex gun. I can understand how in clouds it will pressurize the entire chamber, but in vortex guns you just have your vortex block, and then a bunch of empty space all around. Its the air rushing around in the vortex that pushes the BB out, not the general pressure of the mag and that whole area.
How do you get the pressure to build up behind a BB in a vortex gun?
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Unread postAuthor: jackssmirkingrevenge » Wed Apr 02, 2008 12:55 am

Its the air rushing around in the vortex that pushes the BB out, not the general pressure of the mag and that whole area.
How do you get the pressure to build up behind a BB in a vortex gun?


This is a misconception - the vortex is only there to aid feeding, it's the pressure accelerating the BB down the barrel that gives it its velocity. If what you were saying were true, why bother with a barrel at all?
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