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'New' blow back / forward design

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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Unread postAuthor: The Engineer » Sat Nov 01, 2008 8:20 pm

Yea, I'm working on making a detailed video right now. It has to be extremely detailed for two reasons:

a. The piston cannot actually be seen moving, nor can any of the other parts in the future

b. I can't stand having uncomplete work because it gives me an incomplete feeling
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Unread postAuthor: psycix » Sun Nov 02, 2008 10:47 am

The Engineer wrote:I finally tested my design after adding more epoxy in front and behind the O-ring for stabilty. It also served to add much more weight to the piston. And guess what? It worked! It had a very high rof, so i plan on slowing it down with either a stronger spring or more weight. I also have some plans for a magazine loading system.

Congratulations on your succes!

-Stronger spring: Higher pressure builds up, but the chamber fills up slower so your piston may have too little kinetic energy too slam open.
-More weight: longer opening and traveling times, which may be good. I'd try to add lead to the piston if I were you. Find out weight works best.
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Unread postAuthor: jackssmirkingrevenge » Sun Nov 02, 2008 9:34 pm

The Engineer wrote:And guess what? It worked! It had a very high rof, so i plan on slowing it down with either a stronger spring or more weight.


Sounds like a similar result I got for this one - good luck trying to tame it, kudos to you if you can slow the rate of fire to a practical level but I have my doubts.
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Unread postAuthor: Ragnarok » Sun Nov 02, 2008 9:38 pm

jackssmirkingrevenge wrote:kudos to you if you can slow the rate of fire to a practical level

I'd suggest a slowed air flow and stronger spring - those two factors together could work...
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Unread postAuthor: jackssmirkingrevenge » Sun Nov 02, 2008 9:55 pm

Ragnarok wrote:
jackssmirkingrevenge wrote:kudos to you if you can slow the rate of fire to a practical level

I'd suggest a slowed air flow and stronger spring - those two factors together could work...


My experience with these solutions in various properties is that reducing the airflow has no effect until you reach a point when it just fails to cycle altogether, and a stronger spring doesn't allow the bolt to carry on far enough - hence my scepticism.
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Unread postAuthor: mega_swordman » Sun Nov 02, 2008 11:56 pm

jackssmirkingrevenge wrote:
Ragnarok wrote:
jackssmirkingrevenge wrote:kudos to you if you can slow the rate of fire to a practical level

I'd suggest a slowed air flow and stronger spring - those two factors together could work...


My experience with these solutions in various properties is that reducing the airflow has no effect until you reach a point when it just fails to cycle altogether, and a stronger spring doesn't allow the bolt to carry on far enough - hence my scepticism.


Wouldn't a larger chamber also help with modifying the ROF? The more a chamber has to fill, the longer it will take to cycle.
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Unread postAuthor: kablooie » Mon Nov 03, 2008 2:21 am

Swordman, I think having a larger chamber would just require more air to cycle, and once there was enough airflow to cycle, it would be going at the same speed as a smaller one.

From my own experiences, I'm doubtful that this design will work satisfactorily. Also I agree with Jack, these things have a certain sweet spot where they work, and if you try to slow it down it just doesn't cycle. The only thing I could see working is to add way more weight to the piston. Prove me wrong though, I would be thrilled to see this work, so good luck to ya.
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Unread postAuthor: jackssmirkingrevenge » Mon Nov 03, 2008 3:10 am

kablooie wrote:Prove me wrong though, I would be thrilled to see this work, so good luck to ya.


Same here, no doubt. Unfortunately though, all the times I've dabbled with these sorts of designs it's become patently obvious that a valve which shuts off the air supply while the bolt returns is necessary for reliable and effective function.
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Unread postAuthor: psycix » Mon Nov 03, 2008 5:38 pm

I think the piston travel distance should be increased.
This way the piston has to be accelerated over a longer distance and will also reach a greater speed and thus will slam on further making sure that the hole fully opens.
Increased piston weight would also slow down cycling due to slower acceleration.
Combination of increase of both weight and travel distance would grant the best results.








I think. :D
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Unread postAuthor: The Engineer » Mon Nov 03, 2008 10:30 pm

Good idea psycix. I handn't ever thought about making the actual travel distance of the piston longer. I'll try that out and tell you how it works.
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Unread postAuthor: jackssmirkingrevenge » Tue Nov 04, 2008 12:27 am

psycix wrote:I think the piston travel distance should be increased.
This way the piston has to be accelerated over a longer distance and will also reach a greater speed and thus will slam on further making sure that the hole fully opens.


This will only be relevant for the first shot, as soon as the piston goes past the hole while returning the pressure is going to stop it from travelling much further. The most effective idea is to cut off the pressure feed on the pistons return stroke in order for it not to encounter any resistance on the way back and reseat fully.
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Unread postAuthor: psycix » Tue Nov 04, 2008 2:06 pm

If the pistons weight is large enough (and the air feed low enough) it has enough speed*mass on the way back and will thus take some time to slow down, stop, and go the other way.
This takes some time, lowering the ROF and possibly increasing pressure buildup.

The longer the piston travel, the further he will move on the initial stroke AND the further he will move backwards due to a larger speed. (more distance on the return stroke)
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