Ball Valve strafer prototype

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Postby fullmetaljacket » Mon Mar 07, 2005 7:31 am

Over the weekend I built a prototype, roughly to this <a href="http://pictures.greatestjournal.com/userimg/3431029/512443">design</a>, to test the theory presented <a href="http://localhost/forums/viewtopic.php?t=8652&whichpage=1">here</a>.

<img src="http://pictures.greatestjournal.com/userimg/3464513/512443" width="607" height="198">
Overall view - the barrel is 25 inches long

<img src="http://pictures.greatestjournal.com/userimg/3464526/512443" width="473" height="354">
Closeup of the BB chamber & ball valve.

The rate of fire seems more or less identical to my normal strafer with a blowgun valve, although there were problems with feeding, it still needed shaking quite frequently and I think this strengthens the case for some kind of extrenal agitation.

At 100 psi I ran 4 shot strings of steel and lead BBs through the chrono, got the following velocity figures:

For steel BBs (5.3 grains) - 361 fps, 393 fps, 372 fps, 398 fps

For lead BBs (8.0 grains) - 324 fps, 330 fps, 319 fps, 322 fps

The ball valve system clearly seems to offer better performance as far as velocity is concerned, but it's quite inconvenient to use, especially compared to a 'trigger' type blowgun. Also, the rate of fire is far too high - I'm still after something that will go *dakka dakka dakka dakka dakka* as opposed to *BRAAAAAAAP*, and SPG's recent experiments with a rotary breech seem to suggest this is the way to go, although geared down to a range below 600 rpm.

Edit: note that in the original design concept, the tubing feeding air into the chamber is much wider than the barrel diameter, but in this case, the nozzles at both ends of the orange flexible tubing connected to the compressor are 0.5mm smaller than the barrel diameter. In spite of this, the velocities are over 100 fps faster than the approximate 250 fps average I had obtained with my standalone strafer design.
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Postby ethyl » Mon Mar 07, 2005 7:52 am

This reminds me the drain for a water heater. The sediments gets push out by the water presure.

Why do you need a vortex block, a skirt? The air is entering into the chamber instead of the vortex block. I don't see the need for a vortex block. Your original theory don't have the vortex block too.
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Postby fullmetaljacket » Mon Mar 07, 2005 8:03 am

If the airflow isn't directed in a manner to agitate the BBs, they will simply jam every now and then and the air will simply flow out without firing. Even thought I have a vortex block in this design, it still needs a fairly regular shaking to keep on firing.

If you look at the original concept drawing there's an electrically driven paddle that ensures the BBs are constantly in motion.
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Postby ethyl » Mon Mar 07, 2005 5:08 pm

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Postby syco kilaa » Mon Mar 07, 2005 6:36 pm

ummm, I don't think that will work because the air/bb out put is at the bottom of the vortex block to begin with, so for the bbs to exit the gun they would have to stop and go the other way to exit the vortex, maybe if you just raised the barrel a little bit to the top of the block, but then you have something that looks somewhat like the regular old vortex gun. I guess you can't really beat the good old originals.
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Postby ethyl » Tue Mar 08, 2005 5:54 am

"maybe if you just raised the barrel a little bit to the top of the block"

that's what I intended to do but I didn't have time(i actually forgot to paint it).
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Postby fullmetaljacket » Tue Mar 08, 2005 10:51 am

I don't think either of those solutions would work, because the airway in would in practice be much wider than the barrel outlet and I doubt that kind of airflow would generate a suitable vortex.

I'm currently working on a design that combines the ball valve with the rotating breech in a different manner, more on that later ;)
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Postby syco kilaa » Tue Mar 08, 2005 11:47 pm

riiiiiiiiight, keep us updated
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Postby fullmetaljacket » Tue Mar 15, 2005 4:55 pm

After further testing, some thoughts:

Even with an 'ideal' setup - ie no air pressure wasted filling up the BB chamber - steel BBs appear to have an upper limit of circa 400 fps with 110 psi from a 25 inch barrel. This gives each BB a muzzle energy of slightly less than 2 ft/lbs, roughly the same as a <a href="http://www.kaehny.de/luftdruckwaffen/co2/cp99/cp99_military_offen_vollbild.jpg">CO2 powered pistol</a>. The vortex block strafer I made achieved a mere 0.8 ft/lb at best, yet was capable of tearing through 5/8 inch ply, soup cans etc. with short bursts, purely because of its blistering rate of fire of around 30 BBs per second. Impressive as it is, in the long run I find it very impractical.

I don't think you can really call vortex/cloud designs 'machine'guns - they are brilliantly simple, with no moving parts, with more similarity to a fireman's hose than an M60. What I would eventually like to build is something that is a true 'machine' gun, that feeds individual rounds at a rate of fire of say 2-3 rounds per second. Staying with 110psi and a reasonably long barrel, using BBs this will give little more power than a high end airsoft gun. I am unwilling/unable to up the pressure, so the logical next step is to up the calibre, I'm currently scribbling away at designs along the lines of something using 0.22 pellets as ammunition.
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Postby The Blight » Tue Mar 15, 2005 6:07 pm

fmj, I might send you some designs I have thought of when it comes to fully automatic BB guns. I too want a efficient BB machine gun (that actually has something mechanical in it). I got inspired by the bb gun this guy made with a fire extinguisher tank.

One of the ideas is of a minigun type. farily simple design, but hard to get right.
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