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Adjustable 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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Adjustable BBMG

Unread postAuthor: kablooie » Tue Jun 07, 2011 12:06 am

Hi everyone, this is a project I've been working on for a while, on and off.

It's a really simple concept, it's essentially a ball-detent type bbmg except I used windshield washer hose as the "valve." The hose is extremely easy to work with, and reliably holds bb's to about 100 psi before letting go. Overall, I am very pleased with the windshield washer hose and it's delayed fire effect, because it greatly lowers the ROF compared to a normal BBMG and simultaneously increases the power of each shot. It also conserves air.

The ball valve at the back is used to ease reloading (I put about 50-100 bb's in at a time), the blowgun is the trigger, and the small valve below the blowgun is used to fine-tune the airflow into the gun, and therefore the rate of fire. The power stays the same regardless of airflow due to the windshield washer hose.

I've made one iteration of this gun already, but the goal behind this one was to make a gun that was aesthetically pleasing and ergonomic. The stock is made of two poplar planks that I inletted with a chisel and a Dremel tool. The two sides are held together with 5mm bolts so I can easily tear down the gun to service it (though with the only moving part being the bb's, there isn't much to service).

The gun functions very well, and is a blast to shoot, though it does have issues with feeding consistently. I think it was a mistake to route the air through the bb chamber as I did, as bb's tend to either not feed, or group around the outlet in such numbers as to jam the entire gun. The gun works flawlessy when shooting upwards (so bb's naturally roll backwards and don't jam), but often jams when pointed downwards. I'm considering some solutions, but would love some (easy?) suggestions.

Here are some pictures, a video of it firing is coming along soon!

Image
Image
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Internals:
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The windshield washer hose:
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Not amazing, but not too bad either:
Image
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Unread postAuthor: jackssmirkingrevenge » Tue Jun 07, 2011 12:23 am

Looks good!

I think one of the sources of your jamming problems is the length of "detent", try using a much shorter amount of hose. Forthis one the tube is only one BB long.

Also, cloud BBMGs need space for the BBs to be agitated, you shouldn't fill your chamber more than 75% of full capacity.

If you're using compressor pressures and 0.177" steel BBs, 480 fps is a very good result. You might want to upgrade to a HPA or CO<sub>2</sub> supply for greater velocity, from what I can see everything should take at least 450 psi safely, though the hose might need an upgrade - have you thought of replacing it with an o-ring in a compression fitting?
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Unread postAuthor: cammyd32 » Tue Jun 07, 2011 11:14 am

Great idea! I love the job you have done with that stock I look forward to seeing videos of it firing. :D
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Unread postAuthor: kablooie » Tue Jun 07, 2011 12:26 pm

JSR, the jamming usually results in the gun just spewing air, making me think it's not the hose that's the problem, but who knows maybe I'll try shortening it anyway. I suspect the jamming is caused by all the bb's clustering around the outlet and sort of jamming themselves together, making it impossible for bb's to escape out through the barrel. I'll also try filling the chamber a little less, that will probably help.

And thanks, that's good to hear, I am indeed using .177 bb's at around 100 psi. It's tempting to up the pressure, but my lack of a high-volume hp air source and my aversion to shock pumps makes me want to stick with what I have. Food for thought though.

Thanks for the responses!

Here's the video, the "target practice" segment is from about 40 feet away, and is just to give you an idea of the gun's accuracy. Enjoy!

[youtube]http://www.youtube.com/watch?v=GTPRoZZG0Sw[/youtube]
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Unread postAuthor: jackssmirkingrevenge » Tue Jun 07, 2011 12:43 pm

You have achieved the holy grail of *dakka dakka dakka*, congratulations :)

What's the diameter of the tube before the inlet? if it's around 9mm, that's a recipe for jams - ideally it should be a factor of 1.5 times the ammunition diameter, so in your case 6.75mm or so - any chance of adding an internal tube to choke the diameter and smooth the flow?
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Unread postAuthor: kablooie » Tue Jun 07, 2011 12:58 pm

The diameter of the tube should be around 13mm (it's 1/2" brass pipe), I made it that large in hopes of avoiding the jamming problem altogether, but do you think it's still worth trying to sleeve it down? Hmmm...
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Unread postAuthor: POLAND_SPUD » Tue Jun 07, 2011 1:02 pm

dentent bbmgs would be perfect if they didn't jam... good job but I guess that we're able to come up with a solution to this problem.... jsr will probably post a ton of schematics soon
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Unread postAuthor: Gun Freak » Thu Jun 09, 2011 5:49 pm

Thats pretty cool, I'm working on one very similar! What is the barrel?
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Unread postAuthor: kablooie » Thu Jun 09, 2011 11:28 pm

Thanks, I look forward to seeing yours. The barrel is 1/4" brass tubing, McMaster part #8950K533. I'm pretty happy with it, it's way more accurate than 1/4" brakeline, but loose enough to keep bb's from jamming in the barrel. It does need to be sleeved however to keep it from bending.

I've been super busy lately, but I do plan on trying out different chamber diameters to see if they work (possibly next week), I'd appreciate any suggestions you guys have. Thanks
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Unread postAuthor: jackssmirkingrevenge » Thu Jun 09, 2011 11:45 pm

POLAND_SPUD wrote:jsr will probably post a ton of schematics soon


In a few weeks JSR will actually be able to build the ridiculous sketches he comes up with ;)
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Unread postAuthor: jonesy42 » Tue Sep 18, 2012 11:55 pm

jackssmirkingrevenge wrote:You have achieved the holy grail of *dakka dakka dakka*, congratulations :)

What's the diameter of the tube before the inlet? if it's around 9mm, that's a recipe for jams - ideally it should be a factor of 1.5 times the ammunition diameter, so in your case 6.75mm or so - any chance of adding an internal tube to choke the diameter and smooth the flow?



Hey JSR, i know this is an old thread, but do you know what the inside
diameter of the 1/4 copper tubing used on this rifle is?...Im guessing
around 6.05mm.

Nice work on the rifle too mate, i just spotted it on "random cannons" :wink:
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Unread postAuthor: jackssmirkingrevenge » Wed Sep 19, 2012 12:08 am

jonesy42 wrote:Hey JSR, i know this is an old thread, but do you know what the inside
diameter of the 1/4 copper tubing used on this rifle is?...Im guessing
around 6.05mm.


If I'm not mistaken this is for steel BBs, and you can get copper tubing in 1/4" OD, 4.5mm ID (steel BBs are 4.4mm).
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Unread postAuthor: jonesy42 » Wed Sep 19, 2012 2:40 am

jackssmirkingrevenge wrote:
jonesy42 wrote:Hey JSR, i know this is an old thread, but do you know what the inside
diameter of the 1/4 copper tubing used on this rifle is?...Im guessing
around 6.05mm.


If I'm not mistaken this is for steel BBs, and you can get copper tubing in 1/4" OD, 4.5mm ID (steel BBs are 4.4mm).



Yeah right, i forgot its .177 cal instead of .25 cal, which is what one of my airsoft barrels
is (roughly). The inside diameter of my airsoft barrel is 6.03mm, i use 6mm steel shot, and some will not go down the barrel when you muzzle load it coz its to tight. Mabe ill try
the 6.05mm version next time. The airsoft barrel groups quite well at 20 metres, when using the 14 grain 6mm steel shot.....heaps better than the plastic .25g bb's.
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Unread postAuthor: discasi » Mon Nov 05, 2012 4:46 pm

Hello my name is Discasi and at this moment I am trying to do a Spudgun. I saw your Spudgun and I found it really cool. That why i am asking you, if you could just tell me how you did that gun and could tell me what is the name of all the parts of the gun. And could you tell me how did you cut the wood piece in to two pieces. And how did you dig into the wood so that you can then put the gun and what is the tool that you use. I am really sorry for my English because English is not my first language.

Discasi

Thank you
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Unread postAuthor: archie370 » Mon Nov 05, 2012 5:49 pm

So you want to know every step of this project with all of the parts an info ... Search YouTube for more info and if you still can't figure it out we will help you keep spudding !!!
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