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PostPosted: Tue Jul 23, 2013 10:41 pm 
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So I've been brainstorming alterations to the Nitro Piston (NP) system. I've seen some Delrin looking washers for around the NP rod to help keeping it in place. When I thought about this it sparked an idea. Not sure where its going either so feel free throw wrenches.

I'm thinking about a modified version of this were there is a spring sliding over the NP rod with 2 delrin washers washers on either side. This would provide the stability on the rod as intended with with washers, and the spring could potentially provide extra force on the actual piston? This got me thinking about the compression depth of the NP rod. Obviously too big of a spring would stop the piston from engaging the sear, too small would allow for the spring to recoil along the NP rod after the shot has fired and could either have positive or adverse affects on the recoil thus POI.

So I'm wondering if anyone knows the compression depth of the rod in the NP(regular not xl)?. Yes I could take one of my NP guns apart an start stuffing springs in to see what fits, or slap the NP in the vise and try to compress it manually with a spring compressor. But thats why I joined a forum!

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PostPosted: Tue Jul 23, 2013 11:24 pm 
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Location: Rocky Mtn Hse Alberta
No room for any spring
All used up by nitro piston.
Sorry

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PostPosted: Wed Jul 24, 2013 9:37 am 
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Voltar1 wrote:
No room for any spring
All used up by nitro piston.
Sorry


Are you saying the rod on the NP recesses 100% inside the rod housing? I find that hard to believe considering the washer mod used would become misaligned an cause vast problems. Sounds like you may be misunderstanding what my idea is.

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PostPosted: Wed Jul 24, 2013 11:17 am 
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Do you want to fit a spring around the complete gas ram (kinda like a car where the absorber is inside the spring) or do you want to fit a spring over the rod that comes in and out gas ram only?

The first idea would be pretty useless I think since the spring would only get about half the compression and you would need a smaller gas ram so giving less total output.

The second one would be quite complicated even if useful. How would you time the spring so they would both get at the end of the chamber at the same time? but even then the air volume between the piston and the end of the compression chamber wouldn't change so you wouldn't get more air out. It would only come out harder giving you more recoil...

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PostPosted: Wed Jul 24, 2013 1:47 pm 
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DocGadget wrote:
Do you want to fit a spring around the complete gas ram (kinda like a car where the absorber is inside the spring) or do you want to fit a spring over the rod that comes in and out gas ram only?

The first idea would be pretty useless I think since the spring would only get about half the compression and you would need a smaller gas ram so giving less total output.

The second one would be quite complicated even if useful. How would you time the spring so they would both get at the end of the chamber at the same time? but even then the air volume between the piston and the end of the compression chamber wouldn't change so you wouldn't get more air out. It would only come out harder giving you more recoil...



Yes I was thinking of the latter, spring over rod. I Thought about the timing, that part would be trial and error I guess. I have a couple of old mainsprings I could just cut one down to approximately 8 coils. I feel like if the NP pressure is slightly similar the that of a high end mainspring then they should time out almost the same.
As far as pressure goes I agree theres no change in chamber volume, thus no extra air. I was under the assumption that the faster the chamber can push the air, the harder the pellet will be pushed.
Now the thought of more chamber volume makes me think. What about rounding out the metal on the top of the piston head. That flat circular area in the middle of the piston seal, where they usually have the bleeder hole on non PAL versions. You could possible shave some space out of there?

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PostPosted: Wed Jul 24, 2013 2:46 pm 
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Experience is a great and unrelenting teacher.

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PostPosted: Wed Jul 24, 2013 6:47 pm 
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rawuol wrote:
DocGadget wrote:
Do you want to fit a spring around the complete gas ram (kinda like a car where the absorber is inside the spring) or do you want to fit a spring over the rod that comes in and out gas ram only?

The first idea would be pretty useless I think since the spring would only get about half the compression and you would need a smaller gas ram so giving less total output.

The second one would be quite complicated even if useful. How would you time the spring so they would both get at the end of the chamber at the same time? but even then the air volume between the piston and the end of the compression chamber wouldn't change so you wouldn't get more air out. It would only come out harder giving you more recoil...



Yes I was thinking of the latter, spring over rod. I Thought about the timing, that part would be trial and error I guess. I have a couple of old mainsprings I could just cut one down to approximately 8 coils. I feel like if the NP pressure is slightly similar the that of a high end mainspring then they should time out almost the same.
As far as pressure goes I agree theres no change in chamber volume, thus no extra air. I was under the assumption that the faster the chamber can push the air, the harder the pellet will be pushed.
Now the thought of more chamber volume makes me think. What about rounding out the metal on the top of the piston head. That flat circular area in the middle of the piston seal, where they usually have the bleeder hole on non PAL versions. You could possible shave some space out of there?


That would give you space BEHIND the seal... it wouldn't be of much use.

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PostPosted: Wed Jul 24, 2013 7:14 pm 
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And less compression, so you'll end up slower. The air volume is the limiting factor here, not spring.


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PostPosted: Wed Jul 24, 2013 7:42 pm 
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Voltar1 wrote:
Experience is a great and unrelenting teacher.


Soooo many times, I've proven that to be QUITE correct, Walter!

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PostPosted: Wed Jul 24, 2013 8:40 pm 
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If you have a PAL rated gun there I can't see any improvement adding more spring power but if you wanted to then I would suggest taking the dimensions of your gas spring and matching them to a industrial gas spring, they can be ordered with custom preloades to the point where you will break your gun and beyond.

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PostPosted: Wed Jul 24, 2013 10:06 pm 
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I find this topic quite interesting. I have no idea what this "gas spring" actually is comprised of -- I guess.

I merely thought it was the compression of a tube of gas, that it's "seal" was held back with a diaphram and the sear, released by the trigger to send the plunger forward to compress the air in the cylinder. As I understood it, there was no spring driving a seal forward, only the hollow tube of compressed gas. I did not know adding or increasing "SOME" spring's tension could increase the 'power' of the compressed gas.
I guess I've got it all wrong - I'm sure listening, though.

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PostPosted: Thu Jul 25, 2013 10:39 am 
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I call it a gas spring because the spring action is caused by compressing the nitrogen charge which on some models can be increased or decreased similar to how a Theoben is adjusted with a pump.

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PostPosted: Thu Jul 25, 2013 3:13 pm 
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Well technically it is a spring, even though we tend to think of a metal coil when we say the word spring, it really refers to any device that stores and releases mechanical energy.


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PostPosted: Fri Jul 26, 2013 8:35 am 
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I think it is already at the power limit that the Gamo/B18 tube can produce.

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PostPosted: Fri Jul 26, 2013 4:51 pm 
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Something interesting... I noticed my crosman nitro venom dusk has more stroke length then my benjamin trail np. Under the assumption that the gas springs are the same in both models this would mean the piston is a little bigger in the Benji. After checking the parts list out on the website I noticed the pistons have different part numbers(unlike everything else on the guns).
I had to check some things out.
After ripping them both apart I confirm my suspicions.
The cut out holes on venom piston are closer to the seal then that of the trail's. Also the venom's piston is about 3/4" shorter. So after confirming that the lever assembly is the same on both rifles, this means that the venom piston actually compresses the gas spring more then that of the benji!

So stroke length on these rifles are determined by the distance of the cutout holes and the overall length on the piston. With that being said I had to put the venom piston in the trail to see if there was a noticeable difference.

I don't have a chony yet so the only way for me to gauge fps is by making longer shots, or by hitting objects at a distance to see if there still impacting with the same force.

Long story short, the benji fired JSB Exact Jumbo Monsters @ 73yds though a 1/2" plywood and a full size sunbeam blender. I shot water bottle half filled with sand from 10 paces farther then that, 1 mil dot up. My girlfriend said that the pop from the JSB's hitting the water bottle was louder then my shot.

Overall I think I may just order a Venom Piston for my Trail. After putting the original piston back in, you can feel its lack of umph.

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