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9mm SMG project + other HPA BBMG experimentation

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: jackssmirkingrevenge » Sun Oct 25, 2009 10:50 am

Well, it works, but power is a bit disappointing, it only penetrated one side of a coffee can.

[youtube]http://www.youtube.com/watch?v=2tfNtsXsH-4[/youtube]

Also, since it requires high flow to move the BBs enough in the chamber to ensure feeding, the rate of fire is still unfeasibly high. There is some barrel bulging too, evidence of in-barrel collisions between BBs that I noticed in older projects.
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Unread postAuthor: psycix » Mon Oct 26, 2009 5:27 am

I think it feeds to fast because the barrel port is right on the bottom, with the flow coming from the opposite side. Gravity already puts BB's right in front of the port causing too much ammo getting crammed into it.
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Unread postAuthor: jackssmirkingrevenge » Mon Oct 26, 2009 6:53 am

psycix wrote:I think it feeds to fast because the barrel port is right on the bottom, with the flow coming from the opposite side. Gravity already puts BB's right in front of the port causing too much ammo getting crammed into it.


I don't think this is the case. After all normal clouds usually have the barrel port higher up and still feed tens of rounds per second.

The problem is that the BBs need agitation, this means high flow from the tank and also therefore once you get up to enough pressure to push the BB through the detent, there isn't much pressure drop in the chamber. This means that as soon as the next BB is in the detent, pressure doesn't have a lot to increase before its enough to push it out too.

In conclusion, reasonable rate of fire means low flow, this implies two things:

1) a mechanical detent is not enough, it needs a seal. If air is leaking past the BB in a mechanical detent, chances are at low flow you won't reach the required pressure to fire the BB.

2) the magazine needs to function reliably irrespective of the airflow. The most obvious answer is a spring fed tube mag, something I've been trying to avoid but it appears to be the most reasonable solution.

edit: some fun with HPA and slow motion :D

[youtube]http://www.youtube.com/watch?v=C9ocv_Jktag[/youtube]
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HPATB.GIF
nowt to do with this thread but "hosting" it here for a private message, here's how the HPA setup could be adapted to launcher larger calibre projectiles
HPATB.GIF (27.18 KiB) Viewed 1487 times
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Unread postAuthor: jackssmirkingrevenge » Sun Nov 21, 2010 4:02 pm

I've neglected this platform somewhat so it was worth a re-visit, especially now I have a bigger tank, and following the success I had with this airsoft BBMGit seemed worth making something similar for 0.177" BBs.

[youtube]http://www.youtube.com/watch?v=rqSgkjVSuwo[/youtube]

The seal seems to have worn out fairly quickly, rate of fire was a lot more reasonable before the above testing, but it's quite promising. Eventually I'd like to add an integral suppressor and a weaver rail for a red dot sight, and I'm almost tempted to do a BtB and lop off the end of the barrel to have it the same length as the tank :D
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Unread postAuthor: Brian the brain » Sat Feb 12, 2011 8:26 am

Actually..a true BTB chop would mean the barrel is about 5mm shorter than the reservoir or whatever " under" you have for your " over"

This makes for the most brutal look.


I would think you'd noticed that... :wink:
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Unread postAuthor: jackssmirkingrevenge » Sat Feb 12, 2011 9:38 am

Brian the brain wrote:I would think you'd noticed that... :wink:


Image

I did... but I simply couldn't bear the loss of performance :?

By the way, did you search for "btb" to see where you've been mentioned of late :D
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Unread postAuthor: toogers » Fri Feb 25, 2011 11:44 pm

where do you get your pressure washer handles? all of the ones at my hardware store cost a fortune.
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Unread postAuthor: ilovefire » Sat Feb 26, 2011 12:09 am

try ebay
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why make it if it dosent shoot?
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Unread postAuthor: toogers » Sat Feb 26, 2011 12:11 am

I'm too impatient for shipping.
i know, i should improve my patience.
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Unread postAuthor: jackssmirkingrevenge » Sat Feb 26, 2011 12:24 am

toogers wrote:i know, i should improve my patience.


Yep. This one claims to handle 3000 psi fpr less that $10 posted.
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Unread postAuthor: toogers » Sat Feb 26, 2011 12:44 am

they have those at my hardware store, but i might as well use regular blowguns, those look a little flimsy. not a fan of the air inlet being at the bottom either, i like it to be under the front like on the one used here. (it gives it a shotgun-like feel and there isn't an annoying tank hanging down.)
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Unread postAuthor: jackssmirkingrevenge » Sat Feb 26, 2011 12:50 am

In that case, you can have one for just under $30 posted.
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Unread postAuthor: toogers » Sat Feb 26, 2011 12:55 am

jackssmirkingrevenge wrote:In that case, you can have one for just under $30 posted.


hate to be stubborn, but my hardware store has these and they're out of my price range. still pretty nice, though. i forgot to look on McMaster, I just realized, so i'll check there.

EDIT: they have the same at McMaster-carr for ~$17, so i'll just work on other parts 'til it arrives.
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Last edited by toogers on Sat Feb 26, 2011 1:00 am, edited 1 time in total.
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Unread postAuthor: jackssmirkingrevenge » Sat Feb 26, 2011 12:59 am

Image
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Unread postAuthor: toogers » Sat Feb 26, 2011 1:01 am

jackssmirkingrevenge wrote:Image


huh?
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