Reply With Quoteno drawbacks, as the pellet has long since gone... the ability to close the port in order to acheive this is something I'm working on a design for...Originally Posted by lensman57
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What would be the result of not allowing the piston from touching the port on decompression? Slamming would not take place for sure and the piston would come to a gradual stop rather than a sudden one but what would be the drawbacks? Just asking.
A.G
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no drawbacks, as the pellet has long since gone... the ability to close the port in order to acheive this is something I'm working on a design for...
Always looking for any cheap, interesting, knackered "project" guns. Thanks, JB.
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How would you stop it - without stopping it?
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I think the answer lies in delaying all aspects of recoil until the pellet has gone........any recoil prior to departure can only be reduced/dampened/made more predictable.
I suppose to address piston bounce you need a locking mechanism when the piston reaches the end of its travel?
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Ignorant question, but doesn't the Diana Giss system do this?
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nah, it just cancels out the recoil with two pistons - but it does it very well. I need to find a GISS rifle, sold my pistol ages ago
Always looking for any cheap, interesting, knackered "project" guns. Thanks, JB.
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Not sure how viable it would be or how long it would last but, could some kind of valve be used just in front of the port?How would you stop it - without stopping it?
Something similar to a nonreturn valve used in plumbing. Maybe with a spring stiff enough to only close the valve at the very end of the pistons travel. Assuming this is when the air pressure is at it's greatest.
..... just a very rough idea.
All of the above.
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I seem to recall seing somewhere ages ago that someone tried to use spring loaded ball bearings on a collar around the piston rod that stopped the piston moving backward - it allowed rearward movement for cocking
Maybe I'm imagining things...
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No. Best bet is to put something in the front part of the piston that is capable of absorbing the residual energy (3-5J) of the piston behind it.
In reality, no matter what you do you still need to absorb the momentum of the piston so all you are doing is changing a piston impact in to a softer and longer push of air pressure or a mechanical system on the front of the cylinder.
BB
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assuming that you could create this wall of air that is solid enough to stop the piston in full flow , what would be the difference to allowing the piston to stop against the end of the comp tube ?
from what i understand about the end of the piston's journey , it comes to rest when both peak pressure and the pellet are long gone .
some one else said this , but the pellet is your valve . .....the fit of the pellet can be crucial .
on a long stroke / lightish piston 21mm tx, i can get best part of 100 fps difference with the same pellet but different fit characteristics .....i think bigtoe found this some time ago , on a jsb discussion , i thought he'd gone bonkers ......but it's true
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Unless you go for the Whiscombe opposing piston method with equal masses cancelling each others inertia your always going to have recoil before the pellet leaves the barrel.
As soon as you release the sear the piston accelerates and in line with Newton's work produces an equal and opposite force on the rifle, you could calculate the actual force dependant on piston weight and how many G's it produces, but suffice to say the piston has to move and therefore produce recoil before any air can be compressed, lightening a piston has a possible reducing effect here, but as KE is mass x Velocity squared your going to have to move a lighter piston quicker to generate the energy resulting in probably equal force as the slower heavier one?
This is during the initial phase of course, but I believe most of the tuning we do is based upon the second phase during bounce, so no matter what we do, short of increasing mass of the rifle to absorb the initial force through inertia we cannot eliminate recoil before the pellet leaves the barrel!
Besides which, the art of shooting springers is the ability to work with these forces, and long may it be so, otherwise we may as well buy a Pcp
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Heres one i have thought about, use a spring/piston to charge a chamber that holds the air and then when ready to take a shot it releases the stored air. Pcp with spring charging! Totally pointless but would like to build one just to see what it would be like.
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Just a throught, but pneumatic cylinders have been using piston cushioning for years. May be adaptable to a springer.
https://www.youtube.com/watch?v=U7gYNW8EFUQ
The only thing this will do is spread the piston energy over a longer time than just abruptly running in to the end.
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If the Piston does not come to a sudden stop then a damper maybe needed to stop it oscilating. But the the piston will come to a gradual stop due to the resistance of the compressed air and the spring itself, Me thinks.How would you stop it - without stopping it?
A.G
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When I was a kid I had a Yamaha 100cc dirt bike ( two stroke ), it had a Reed valve arrangement between the carb and the intake chamber so there wouldn't be a blow back into the carb itself. It was just some very thin leaves of steel on a plastic wedge but they worked brilliantly.
A.G
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