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making the blow-forward breech work

This area is for the discussion of BB or airsoft sub machine guns, and or other small arms such as pellets.
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making the blow-forward breech work

Unread postAuthor: jackssmirkingrevenge » Sun Jan 27, 2008 5:38 am

I've made several attempts at a blow forward breech that would cycle automatically as long as there was airflow, however so for my attempts have either resulted in a valve that hangs open or cycles so fast it's impossible to reload ammunition.

Following the logic that's been developed with the auto-piston discussions, it would appear to me that the simple solution would be to add a check valve that could cut off the flow once the bolt starts moving forward, with the added provision of a firing chamber holding enough air for a good shot.

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Unread postAuthor: ALIHISGREAT » Sun Jan 27, 2008 5:44 am

yet another complicated design from JSR :roll: well i suppose it could be made to work but depending on the operating pressure you might need a pretty heavy bolt to be able to open the check valve for long enough to get some good power.
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Unread postAuthor: jackssmirkingrevenge » Sun Jan 27, 2008 5:52 am

If I wanted to keep things *that* simple, I would have stuck to clouds :P

It could be slightly modified like the diagram below, this would effectively combine the "pop-off" effect in the auto-piston while using the piston motion to directly work the bolt and seal the breech.
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Unread postAuthor: ALIHISGREAT » Sun Jan 27, 2008 7:04 am

how would you start it cycling though? because if you turn on the air the check valve might just close instead of enough air getting through to push the piston forwards.
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Unread postAuthor: VH_man » Sun Jan 27, 2008 7:37 am

I like it JSR....... Its like the pop-valve and the breech turned into one single beautiful machine.......

i swear, every time i think you have it perfect you make it more perfect........

anyway, I am actually constructing one of those snap valves, Im making a Full-Auto Paintball gun :D And mabey putting some electronics in so that i have a fast trigger pull and i can get semi-auto for legitemate feild play....

oh and i will be able to switch the barrel out for a .177 cal BB barrel/breech and a 6mm Airsoft barrel/breech.

Ahhh ideas ideas. Anyway this new idea is quite astounding. You could technically make an automatic Airgun whos receiver (no barrel) couild fit in the palm of your hand.................
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Unread postAuthor: )DEMON( » Sun Jan 27, 2008 8:10 am

To be honest I don't think this design will work very well. It does not seem like the bolt will keep the check valve open long enough to fill the chamber to a decent pressure, unless the check valve is high flowing and the bolt has some weight to it. Even then I think it may just not work.

If you increase the weight of the bolt you need to have a stronger spring and for a stronger spring you need more air pressure, which will result in the check valve being harder to open.

You might get it to work though.
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Unread postAuthor: jackssmirkingrevenge » Sun Jan 27, 2008 8:16 am

Altered the animation slightly to suit a pop-off style bolt - this way, it doesn't make a difference what flow you have in the chamber, it will always work (though changing the flow alters the rate of fire)
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Unread postAuthor: ALIHISGREAT » Sun Jan 27, 2008 8:57 am

yeah that has more chance of working... but it would be a bit faffy to get good performance because of spring strength etc. and a high operating pressure.
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Unread postAuthor: MaxuS the 2nd » Sun Jan 27, 2008 10:45 am

Indeed, spring strength will be critical.
But I like it.
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Unread postAuthor: bigbob12345 » Sun Jan 27, 2008 10:56 am

That is very clever but I think it would cycle too slow for it to be worthwhile but that depends on the amount of flow going into it and I dont know where you would get the extremely strong spring that would be required.
If all the above does not apply at all then ignore this because I am no expert on things like this.
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Unread postAuthor: Antonio » Sun Jan 27, 2008 11:07 am

Hey jack, this design is similar to that I came up with in my P.4 project. In my case the barrel is moving as well, which makes things a bit easier in my case. I might step to ur internal moving part as well, but the problem is finding a spring that fits inbetween all those pipes.
My animation made in interactive physics:
[youtube]http://www.youtube.com/watch?v=0hpY3z1Dux0[/youtube]
Picture:
Image

So I am positive that this gun works. I have already tried to make it without a breech but again the pressure and the springs are hard to ballance. Hope to share some thoughts about this one as it more feasible for my technology'' :)

bigbob12345 wrote:it would cycle too slow for it to be worthwhile but that

)DEMON( wrote:Even then I think it may just not work.
.

ALIHISGREAT wrote:yeah that has more chance of working... but it would be a bit faffy to get good performance because of spring strength etc. and a high operating pressure.


The Physics of this type of valving system:
Impulse of the hammer just before it opens the valve = m*v
Impulse the hammer needs to have to recock= P*A*t (P=pressure, A= area of the backside of the bolt, t=dwell time)
Inorder for autorecocking P*A*t > m*v
Then you have another factor; the hammer needs to open the valve first.
The Force the valve has = P*A
The Force the hammer needs to have to open the valve =m*a
a (acceleration of the hammer)= v/(m/k)^0.5 (k= the spring constant of the hammer spring)
So for a balanced airgun (autorecock) the hammer needs to have these properties:
P*A*t>m*v
P*a>m*v/(m/k)^0.5
(Btw this all formulae doesnt include the spring behind the poppet valve)
Now I hope this gives everybody some thinking space and hope for this design. Atleast we dont get to say now "it may or may not work". We have a certain boundaries where we have to be in and I listed those above.
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Last edited by Antonio on Sun Jan 27, 2008 11:26 am, edited 2 times in total.
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Unread postAuthor: BigGrib » Sun Jan 27, 2008 11:15 am

ok you need to put a spring on the opposite side of where the spring is now, one that is not as strong as the one in there now but iust one that you can adjust the compression on to provide a damper to slow the plunger down so you can slow down your rate of fire without effecting your airflow. that way you can slow the mechanism eough to effectively load ammo.
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Yea, that's definitely going to get you at least a tazer.

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Unread postAuthor: Antonio » Sun Jan 27, 2008 11:32 am

BigGrib wrote:ok you need to put a spring on the opposite side of where the spring is now, one that is not as strong as the one in there now but iust one that you can adjust the compression on to provide a damper to slow the plunger down so you can slow down your rate of fire without effecting your airflow. that way you can slow the mechanism eough to effectively load ammo.


Another spring would not act as a damper. A spring is depicted as a thing that is length depended not time or speed depended like a damper. So it would rather desturb the cycling then correct it to lower rates of fire. In jacks working prototype air is used; that can be seen/used as a damper. The smaller passage to second reservour acts like a time delay. I am not sure if we can c that in these designs. (if you guys know what I mean, its kinda tricky to explain. But you have to c it as a system built up of different subsystems. In jacks newer working prototype he has two systems, in this case only one. So I dont think rate of fire can be controlled except by seazing the flow. The autobreech is reactive so thats why I think it can all be seen as one system> valve and hammer.
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Re: making the blow-forward breech work

Unread postAuthor: Antonio » Sun Jan 27, 2008 11:36 am

jackssmirkingrevenge wrote:I've made several attempts at a [blow forward breech


Btw jack is this a breech now or a standalone system? I dont get how this would work with your other prototype u made as it has no way of running in synchronize.
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Unread postAuthor: BigGrib » Sun Jan 27, 2008 11:41 am

ant wrote: its kinda tricky to explain.


Yeah you should try a little harder cause I have no clue what the hell you're talking about
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Yea, that's definitely going to get you at least a tazer.

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