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6mm Semi-auto : Fully working blow-forward, 150 RPM + Vids

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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6mm Semi-auto : Fully working blow-forward, 150 RPM + Vids

Unread postAuthor: Leonard » Fri Jul 18, 2008 5:57 pm

6mm Semi-auto : Fully working blow-forward bolt, Approx 180 RPM

I proudly present you the working version of the project i have been working on for quite a while, please bare with the poor aestetics, this is the beta version of a desing that i plan to incorporate in a more convenient form :

Image

First of all i'd like to thank JSR for sharing his work on the blow-forward bolt/piston on this forum, his work obviously inspired most this launcher.

Here is a quick diagram of the inner parts of the gun :

Image

As many will notice, there is nothing realy new in this desing, at first it may look very simple, but the version of the launcher is actually the fourth try at getting a reliable, quick and stable semi-auto mecanism. My main problem in the construction of the launcher was :

- The only epoxy availble in Canada is epoxy putty, so all casting using epoxy is very hard or simply impossible for me.

- I have access to no specific tools exept a drill.

One may say that i could have simply bough the missing tools and ordered some low-viscosity epoxy, but i actually wanted a mecanism that was simple to make and did not required any special machining. The first desing i wanted to make was this one :

Image

It is exacly JSR's semi-auto on this page :

http://www.spudfiles.com/forums/6mm-sem ... 10075.html

My version of it unfortunatly never worked properly, i had exacly the same problem that JSR had when he made the original device. The rate of fire was terrible because the bolt would take an awful lot of time to reset back in it's first position. The reason why was that the piston was heavy to move and could not gather any momentum, so the air simply leaked slowly into the bolt. To solve this problem, i needed a desing that would allow air to be contained in a "secondary" chamber so that the bolt reset's automaticaly. Hence the setup that was used on the present launcher :

Image

Image

Image

Image

When the bolt move forward, it as enough momentum so that almost all air dump into the secondary chamber. From there, the air can go trough the bolt and push the projectile. Unfortunatly, this design cut the pressure in half, resulting in relatively weak power overall. But when i built it, i was looking for ROF, not power, and i feel i kinda reached my goal.

Here's a quick video of the launcher bolt movement and the launcher shooting at different speed.

EDIT : Image

Even though this is a working device, it as the disadvantages of not being able to go full auto under a constant flow of air and a noticeable lack of power. I do not think that the blow-forward bolt is the solution to reach full auto, the problem being manly the spring, wich need to be choosen carefully so that it's strengh allow for a reciprocation of the bolt/piston.

I had an idea of a springless bolt, based on the inline valve, wich i will open a thread about it later.



I would very much like to hear what the members think about this, i will be glad to accept every single comment, would it be good or bad. Thanks for reading!
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Last edited by Leonard on Sat Jul 19, 2008 1:19 am, edited 2 times in total.
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Unread postAuthor: Sticky_Tape » Fri Jul 18, 2008 6:41 pm

Fiber glass resin is good as a casting epoxy I live in Nova Scotia I get it at walmart another good casting epoxy for small scales is the tubed epoxy it is exspencive if you get it at the wrong place. I can get it at a dollar store the tube is 25ml and at walmart you can get the brand named tubed epoxy 25ml for 6 bucks. The dollar store epoxy works just as well I tested.
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You can tell how awesome a cannon is by the pressure used.
http://www.spudfiles.com/forums/high-pr ... 12803.html
xnt rnm ne z ahtbg
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Unread postAuthor: Hawkeye » Fri Jul 18, 2008 6:49 pm

You can buy Epoxy of all sorts everywhere in Canada. Canada has boatbuilding supplies spilling over its borders.
iI'm not sure where you live but any marine store will have Epoxy. Most woodworking stores as well.
In fact I wouldn't be surprised if Canada is near the top of the list for quantity of liquid Epoxy used per annum.
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Unread postAuthor: Sticky_Tape » Fri Jul 18, 2008 6:55 pm

I would say that there is more boat building stores near water instead of the inlands
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You can tell how awesome a cannon is by the pressure used.
http://www.spudfiles.com/forums/high-pr ... 12803.html
xnt rnm ne z ahtbg
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Unread postAuthor: Leonard » Mon Jul 21, 2008 10:37 am

Sticky_Tape wrote:Fiber glass resin is good as a casting epoxy I live in Nova Scotia I get it at walmart another good casting epoxy for small scales is the tubed epoxy it is exspencive if you get it at the wrong place. I can get it at a dollar store the tube is 25ml and at walmart you can get the brand named tubed epoxy 25ml for 6 bucks. The dollar store epoxy works just as well I tested.


I'll look into that. I must say i dont live close to the ocean. By "tubed epoxy", do you mean epoxy putty? If so, that's what i use.
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Re: 6mm Semi-auto : Fully working blow-forward, 150 RPM + Vi

Unread postAuthor: jackssmirkingrevenge » Mon Jul 21, 2008 6:51 pm

Leonard wrote:Even though this is a working device, it as the disadvantages of not being able to go full auto under a constant flow of air and a noticeable lack of power. I do not think that the blow-forward bolt is the solution to reach full auto, the problem being manly the spring, wich need to be choosen carefully so that it's strengh allow for a reciprocation of the bolt/piston.


We seem to have come to the same conclusions, but at least you have a working semi-auto, which is more than many on here can claim ;)

Well executed and keep up the good work :)
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Re: 6mm Semi-auto : Fully working blow-forward, 150 RPM + Vi

Unread postAuthor: Ragnarok » Mon Jul 21, 2008 6:53 pm

jackssmirkingrevenge wrote:But at least you have a working semi-auto, which is more than many on here can claim.

I'm working on it ;)
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Does that thing kinda look like a big cat to you?
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Re: 6mm Semi-auto : Fully working blow-forward, 150 RPM + Vi

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Unread postAuthor: Sticky_Tape » Mon Jul 21, 2008 7:01 pm

Leonard wrote:
Sticky_Tape wrote:Fiber glass resin is good as a casting epoxy I live in Nova Scotia I get it at walmart another good casting epoxy for small scales is the tubed epoxy it is exspencive if you get it at the wrong place. I can get it at a dollar store the tube is 25ml and at walmart you can get the brand named tubed epoxy 25ml for 6 bucks. The dollar store epoxy works just as well I tested.


I'll look into that. I must say i dont live close to the ocean. By "tubed epoxy", do you mean epoxy putty? If so, that's what i use.

I meant like syringe tube epoxy I wouldn't have mentioned it if it was putty.
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You can tell how awesome a cannon is by the pressure used.
http://www.spudfiles.com/forums/high-pr ... 12803.html
xnt rnm ne z ahtbg
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Re: 6mm Semi-auto : Fully working blow-forward, 150 RPM + Vi

Unread postAuthor: jackssmirkingrevenge » Mon Jul 21, 2008 7:06 pm

Ragnarok wrote:I'm working on it ;)


Theories don't count :p :) off topic, I was in the capital of your lovely country for the weekend, I creamed my pants several times while touring the Imperial War Museum, great stuff :)
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Re: 6mm Semi-auto : Fully working blow-forward, 150 RPM + Vi

Unread postAuthor: Leonard » Mon Jul 21, 2008 7:25 pm

jackssmirkingrevenge wrote:
Leonard wrote:Even though this is a working device, it as the disadvantages of not being able to go full auto under a constant flow of air and a noticeable lack of power. I do not think that the blow-forward bolt is the solution to reach full auto, the problem being manly the spring, wich need to be choosen carefully so that it's strengh allow for a reciprocation of the bolt/piston.


We seem to have come to the same conclusions, but at least you have a working semi-auto, which is more than many on here can claim ;)

Well executed and keep up the good work :)


Thanks for the words, im glad you stumbled across this thread. Are you still working on a full-auto setup? If so, and if you have time, i'd like you to take a look at this and tell me what you think :

http://www.spudfiles.com/forums/semi-fu ... 15364.html
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