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Auto-Ram BBMG

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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Unread postAuthor: Carlman » Wed Aug 20, 2008 11:33 am

if you were to turn down the flow of the incomming air would it not help feeding as lower rof?
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Unread postAuthor: kablooie » Wed Aug 20, 2008 12:19 pm

Thanks guys for all the feedback, I'll try and answer all your questions.

In the Diagram, the bolt looks like it passes through the magazine because originally, my plan was to attach a powerful neodymium magnet to the ram that would pass over the magazine and stop the flow off bb's. That didn't work so well, the air rushing through the magazine combined with the magnet's pull made it work only sometimes (but it did occasionally work :P ).

The reason I made the ram in the first place, was to try and achieve rotation of a flywheel. I have no access to a lathe, milling machine, or anything, so my best attempt involved legos and lots of them. It didn't work. The concept is so simple, but it is extremely hard to pull off.

The power of it (at 60 psi) varies a lot, as you can see in the video, the ram will cycle at different speeds, and extend more or less (or not at all) depending on how far I open the ball valve. So far the most power I've gotten out of it was it was able to pierce a soda can about 8 times, and about three of those shots exited the can. In the video, you can't really see, but the bb's were going through the paper and into (almost through) the double-thick cardboard on the other side. Not exactly awesome power, but more could be achieved.

Giving ram less air to operate on only works up to a point, because what you were seeing in the first part of the vid, was it operating on the minimum amount of air it will take.

I will be gone for most of today, but I plan to continue to fiddle with this gun and get back to you with the results. If you have any more questions, feel free to ask.
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Unread postAuthor: jackssmirkingrevenge » Wed Aug 20, 2008 1:04 pm

This is about as uncomplicated as things get:

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Certainly a good effort, but as beautifully simple as it looks on paper, I doubt it will ever work well that way. Looking forward to be proved wrong though ;)
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Unread postAuthor: Antonio » Wed Aug 20, 2008 1:19 pm

jackssmirkingrevenge wrote:
If you're referring to this project, it actually did reciprocate, but too fast to be useful in terms of power or practicality. Clide reported similar results with the blow-forward bolt in his golf ball semi while he was experimenting with it. After endless hours of using different spring strengths and lengths as well as bolt weights, I still got the same results - it either reciprocates too fast - the same "angry wasp" effect - or not at all.



I have been working on the blowback breech system but it as well doesnt have enough power once it has pushed the breech back. So mine had a piston going forwards hitting a valve. When the piston hit back due to the pressure it would go past a vent that would vent the air to the barrel(above> like a stacked tube). The recocking of the psiton took too much energy though (as though it did cycle)> the burst of air out of the vent was way too weak and had way too little volume''. I think I should also make a post of that sometime
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Unread postAuthor: Brian the brain » Wed Aug 20, 2008 1:23 pm

Snapvalve actuated, modded qev works really well.

But I'll post more about that once I can turn some quality snapvalves on my bro's lathe.

Great for larger ammo.Venting pilot volume when you're shooting bb's is not desirable.
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Unread postAuthor: jackssmirkingrevenge » Wed Aug 20, 2008 2:16 pm

Brian the brain wrote:Snapvalve actuated, modded qev works really well.


Remind me, had the snap-valve as actual firing valve worked?
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Unread postAuthor: trollhameran » Wed Aug 20, 2008 2:31 pm

Do you that maybe the blow forward design would work better on a larger scale? everything would be bigger so it would have more travel, and the projectiles would be somewhat heavier than bb's so the added weight plus a spring/plunger in the mag would perhaps make loading faster a possibility.
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Unread postAuthor: jackssmirkingrevenge » Wed Aug 20, 2008 2:48 pm

I doubt it, according to clide it didn't work with his GB semi and that's well, golfball calibre.
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Unread postAuthor: POLAND_SPUD » Wed Aug 20, 2008 2:54 pm

Remind me, had the snap-valve as actual firing valve worked
AFAIK it didn't but what's wrong with a QEV&pilot valve combo ? sure it's not perfectly effiecient but there are hardly any easy ways of making a cheap powerfull semi or auto gun
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Unread postAuthor: trollhameran » Wed Aug 20, 2008 3:05 pm

I have a design for a cheap powerful semi, that should be efficient, as the only air that leaves it, goes out the barrel, it involves two pistons joined by a rod, a very small amount of dead space, and a manually operated bolt, did make a prototype a while ago, its posted on here somewhere.
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Unread postAuthor: kablooie » Wed Aug 20, 2008 11:05 pm

Success! The bb gun now empties all 15 or so rounds very quickly and consistently, I am not sure whether or not the feed completely matches the ram's air output, but it has to be close. Looking at the video I made last night led me to the conclusion the that the bb's were being pushed upwards in the magazine by the pulses of air, so I used a very thin hose (a Lego one :roll: it was what I had..), to route some of the air from the ram output to the top of the magazine, to counter the air coming from below (if that makes any sense).

Here's a pic of the new setup, again, some hot glue and tape is involved, but whatever, it's a prototype. If more than one person wants a vid (for proof, reference, whatever) I will be happy to make one.
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Notice the new hose... and my foot (for JSR and co.)
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Unread postAuthor: jackssmirkingrevenge » Wed Aug 20, 2008 11:12 pm

Nooooo, not teh feets!

and yes, a vid would be cool :)
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Unread postAuthor: kablooie » Thu Aug 21, 2008 12:52 am

Well, I went ahead with the video despite what I said above (about the more than one person thing). Here ya go, please tell me what you think.

A few notes about the video are:
-I apologize for the blanket in the frame, but you can still see everything just fine.
-You can see/hear the gun running (sounds like an air compressor kind of, which is ironic because I don't have one...) before the bb's start shooting, that's because I put a magnet on the magazine to let me adjust the rof before wasting all of my bb's
-The small magazine that I am using now holds only 19 bb's, that's why there aren't a million bb's shooting out.


[youtube]http://www.youtube.com/watch?v=xnk5sQNiIM0[/youtube]
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Unread postAuthor: trollhameran » Thu Aug 21, 2008 12:55 am

A vid would definitely be cool, I could never find a hose the right size to do that with the mag, although I have thought of it before.

Edit: nice video, looks like you've got it working quite well now, you just need a bigger magazine :D

Second edit: I have often thought, why not use a cheap jigsaw to move the ram back and forward, they're quite bulky but the movement is perfect and you can control the speed.
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Unread postAuthor: kablooie » Thu Aug 21, 2008 1:33 am

A Jigsaw is a good idea, it would allow for pretty much ideal control until the pressure becomes too much for the jigsaw, but I'm not sure I will use it because I don't really have much of a budget for this project, and it would be very bulky. At some point, however, I might give it a try, because that would give this an edge over a normal bbmg (besides the cool factor and the awesome noise).

Another plus to this design is that in my experience so far, the auto-ram uses less air than a cloud (haven't tried a vortex) that I made out of a small soap bottle. I have a feeling though, that once I get the power equivalent, they will consume almost the same amount of air.

I wish the contest would start soon... not necessarily for this project though.
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