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full-auto breech :D

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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full-auto breech :D

Unread postAuthor: jackssmirkingrevenge » Sun Aug 26, 2007 6:45 am

Following on from my original idea for a full auto blow forward breech that was a bit of a flop, I decided to take a slightly different approach with version 2 to this design:

Image

Here's the parts before assembly, with the bolt and spring removed:

Image

And here it is in action. I wish I could show you videos with sound because it's a truly impressive jackhammer noise :D The bolt is hard to see as it cycles so quickly, I hope this won't be a problem when it comes to feeding ammunition. I'm going to experiment with a stiffer spring to see if I can slow it down a little.

[youtube]http://youtube.com/watch?v=i9e_ZOfEE3E[/youtube]


[youtube]http://youtube.com/watch?v=V65z_w0Ftc4[/youtube]

watch this space for further development :)

The actual firing setup is attached below:
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breech attached to blowgun
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Unread postAuthor: joannaardway » Sun Aug 26, 2007 7:28 am

Excellent, once again.
The ratio of between the number of concepts of yours I want to copy, and the number you churn out is somewhere above 90% - you have great ideas, but I just don't have the financial situation to steal them... oh well.

If you could get a sound recording of it in operation, it could be possible to estimate the potential ROF you'll acheive there.
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Unread postAuthor: jackssmirkingrevenge » Sun Aug 26, 2007 7:36 am

cheers :)

My ideas are for the people, feel free to appropriate them whenever you have the resources.

I've done some further testing (until I broke the bolt hook again hehe, it never fails to amuse me flying out of the barrel) and it's clear that even with a stiffer spring, the rate of fire is much too high, not only for feeding purposes but also to allow the projctile to leave the barrel in time. I could shorten the barrel but I would rather not. As it is, single shots with an airsoft BB didn't have enough energy to make a hole in a sheet of corrugated card.

There's also considerable stress on the spring, see the attached image of what the original looked like after a few burts of firing (especially compared to its unused state above). I tried a stiffer spring, the stiffest I had but pretty much the same rate of fire and same effect on the spring.

I was thinking of rubber bands as a possible alternative, there's still a lot of R&D to go
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bolt and spring, before the bolt hook attachment decided to come off again.
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Unread postAuthor: Marco321 » Sun Aug 26, 2007 7:47 am

There is some amazing work you have produced, I'm truly amazed. I cant wait to see your new ideas and developments of your guns. Really good work on this one, i love the idea!
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Unread postAuthor: Hailfire753 » Sun Aug 26, 2007 7:49 am

Wow, Great idea!. Just be carful not to lose the "blow-foward" part if it flies out of the barrel!
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Unread postAuthor: jackssmirkingrevenge » Sun Aug 26, 2007 8:06 am

Cheers for the comments :)

Just be carful not to lose the "blow-foward" part if it flies out of the barrel!


That's why I aimed the barrel at an old curtain, in spite of the fact I knew there wasn't any ammunition loaded.
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Unread postAuthor: clide » Sun Aug 26, 2007 5:46 pm

Nice work.

That video reminded me of something that I had completely forgot about, I hooked the blow forward bolt when I first built it for the Slider up to my air compressor and got the same jackhammer effect, but just like yours it was way to fast to load ammo.

I think the idea does have potential though. Another construction method you might consider is cutting two slits across from each other in the barrel and running a rod through the bolt that extends out the slits. You could attach a spring to each side of the rod, and it would also serve as a physical stop so that your bolt won't go too far forward and break the springs.
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Unread postAuthor: jackssmirkingrevenge » Sun Aug 26, 2007 6:03 pm

Thanks for the comments clide, since this design is essentially the same as your GB-semi breech with the exception of spring location, I was wondering if you ever observed the same effect.

I'm starting to come to the conclusion that this is going to be too hard to fine tune - as it is, the bolt starts to cycle way before the projectile has had time to leave the barrel - and I should start pursuing the pop-off-valve-in-the-pilot-chamber approach to "pulse" the air fed to a blow-forward breech.
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Unread postAuthor: clide » Sun Aug 26, 2007 6:55 pm

jackssmirkingrevenge wrote:Thanks for the comments clide, since this design is essentially the same as your GB-semi breech with the exception of spring location, I was wondering if you ever observed the same effect.

I'm starting to come to the conclusion that this is going to be too hard to fine tune - as it is, the bolt starts to cycle way before the projectile has had time to leave the barrel - and I should start pursuing the pop-off-valve-in-the-pilot-chamber approach to "pulse" the air fed to a blow-forward breech.


Right, as it is now the bolt will start trying to close as soon as it is open. One way to get around this would be to make a disk in the larger diameter area, and put some vent holes on the other side of the disk so pressure doesn't build as the bolt moves forward. Once the bolt unseals from the rear tube, the disk in the larger diameter area will be exposed to the pressure and will hold the bolt forward until there is a certain pressure drop. You would want the surface area of the disk to be at least bigger than the surface area of the bolt, and the bigger it is beyond that, the more pressure drop required before it closes. Say you make the disk twice the surface area of the bolt, then the valve bolt will start to close at about half of the pressure it initially opened at is left. I was working on concept a bit like this that lead to the GB Semi, but I think it was a poor choice for me to start at golf ball scale. At your scale I think the idea could work.
A small chamber with fed by a flow controlled blowgun would give you power and allow for an adjustable ROF.


Of course with your construction methods, such a design would leave the bolt unable to be removed for service, but if you also put the springs on the outside with a method like I mentioned above then you could adjust those.

I could draw a picture if you don't quite get what I'm trying to explain.

Also, I found a video that I had sent to chewy about the auto cycling Slider bolt. I'll try to post it in a bit because it does sound pretty cool.

Edit: Here is the video. Of course that is way too fast to be any good, but that is mainly because of the weak spring...It wasn't built or intended to do this so that is why the spring is weak. Sounds like a little engine.
http://video.google.com/videoplay?docid ... 9687&hl=en
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Last edited by clide on Sun Aug 26, 2007 7:24 pm, edited 1 time in total.

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Unread postAuthor: Novacastrian » Sun Aug 26, 2007 9:15 pm

The legend has struck again, i wonder what Jacks dreams are like.... Maybe somthing like, mmm epoxy,mmm pvc, mmm, compressed air, and then someones voice " Jack get your hand off it, it's time to get up for work!!" :lol:
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Unread postAuthor: iknowmy3tables » Sun Aug 26, 2007 9:28 pm

its a nice pice of work but idea this looks just like your blow forward bolt clide this is an existing concept
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Unread postAuthor: experament-u2 » Mon Aug 27, 2007 12:38 am

clide wrote:Here is the video. Of course that is way too fast to be any good, but that is mainly because of the weak spring...It wasn't built or intended to do this so that is why the spring is weak. Sounds like a little engine.
http://video.google.com/videoplay?docid ... 9687&hl=en


that sounds so awesome clide
your slider was one of the guns that got me interested in spudguns :D

oh and jack great work, your on the road to success but its a little bumpy at the moment but soon you will get it right keep trying and good luck

U2 out
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Unread postAuthor: jackssmirkingrevenge » Mon Aug 27, 2007 1:41 am

iknowmy3tables wrote:its a nice pice of work but idea this looks just like your blow forward bolt clide this is an existing concept


The blow-forward valve was patented over ten years ago, what's your point?

Here is the video. Of course that is way too fast to be any good, but that is mainly because of the weak spring...It wasn't built or intended to do this so that is why the spring is weak. Sounds like a little engine.
http://video.google.com/videoplay?docid ... 9687&hl=en


That's pretty much the effect I'm getting. Your idea sounds like it would work though, back to the drawing board :D

edit: thinking about it though, wouldn't the result be basically similar to my first design? I don't think this will work effectively with a constant flow.
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Unread postAuthor: clide » Mon Aug 27, 2007 6:46 pm

jackssmirkingrevenge wrote:That's pretty much the effect I'm getting. Your idea sounds like it would work though, back to the drawing board :D

edit: thinking about it though, wouldn't the result be basically similar to my first design? I don't think this will work effectively with a constant flow.


Not really, your first design suffers the same problems as this one (if you had a stronger spring). The bolt will start trying to return as soon as it opens and the design relies almost entirely on inertia to cycle properly. With the design I was describing, the bolt will want to move forward more as soon as it opens the air path, and should stay forward until it will easily and fully return. It relies more on the changing air pressures and surface areas (like a piston valve) to cycle rather than the inertia of the bolt.
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Unread postAuthor: Fnord » Mon Aug 27, 2007 7:17 pm

Maybe I've missed something in the jumble of posts above, but wouldn't a simple way to limit the rpm's (and therefore allow the ammo to fall into place more easily), be just to reduce the flow?
It would also reduce the stress on components and lead to fewer failures (A blowgun puts out quite a bit of air for something that small to handle:)

Other than that it's a nice and simple design tha I might copy/manipulate sometime in the future.
Good job. :happy11:
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