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This is not a hammer debounce device

June 11 2012 at 10:27 AM

  (Login Dnadnnoid)
Crosman Forum Member
from IP address 98.232.166.154

because the hammer still bounces, just not against the stem

[IMG][linked image][/IMG]

[IMG][linked image][/IMG]

i cut off about 4.5 coils from a 1377 valve spring and glued it to a washer/rivet thingy. using double sided tape i stuck it to the outside of the valve. the theory was to absorb most of the hammers energy before it even touched the stem and it seems to work. now it just taps the stem and my valve retains quite a bit of air.

i get two decent shots. the first one being the most powerful and the second shot loses about 200-230 fps. then i have to actually dry fire it TWICE to get the remaining air out. now i just need to get a lighter hammer and figure out a way to make a spring adjuster for it

let me hear what you guys think. I know some of you are very well educated in the physics of this type of stuff. i think it could be improved a bit

oh btw i switched hammer springs too. i used a 2240 spring


DNADNNOID


    
This message has been edited by Dnadnnoid from IP address 98.232.166.154 on May 12, 2013 10:32 AM
This message has been edited by Dnadnnoid from IP address 98.232.166.154 on Jun 11, 2012 10:31 AM
This message has been edited by Dnadnnoid from IP address 98.232.166.154 on Jun 11, 2012 10:28 AM


 
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AuthorReply


(Login pneuguy)
Crosman Forum Member
98.69.174.37

Well, the thing is: Springs don't dissipate energy. They store it and then give it back.

June 11 2012, 10:39 AM 

I'm sure you're right that your spring buffer accepts a lot of the hammer's energy and prevents it from making it to the valve stem. But then it gives that energy back to the hammer in the form of a more violent bounce.

So my question would be, what prevents that added bounce energy from rebounding from the hammer spring, then driving the hammer back to compress the buffer spring and hitting the stem again?

Steve

 
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(Login Dnadnnoid)
Crosman Forum Member
98.232.166.154

Re: Well, the thing is: Springs don't dissipate energy. They store it and then give it back.

June 11 2012, 10:41 AM 

because the top of the spring sits far enough away from the stem that any bouncing that occures doesn't transfer onto the stem. you should try it happy.gif

 
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(Login Dnadnnoid)
Crosman Forum Member
98.232.166.154

only the initial hammer strike has the energy to compres the spring enough to hit the stem

June 11 2012, 10:45 AM 

the 1377 valve spring is very stiff!

 
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(Login pneuguy)
Crosman Forum Member
98.69.174.37

Thanks, but years ago I did lots of experimentation with valve stem buffers.

June 11 2012, 11:09 AM 

Eventually I understood why they don't - and can't - work very well.

Steve

 
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(Login Dnadnnoid)
Crosman Forum Member
98.232.166.154

so tell us about it

June 11 2012, 11:15 AM 

instead of being all smug about the fact you did it first

 
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(Login pneuguy)
Crosman Forum Member
98.69.174.37

I just did. To sum up: My experience is that springy buffers are

June 11 2012, 11:22 AM 

...essentially exactly the same in effect as reducing the energy of the hammer strike by any other means - e.g., by reducing the rate or preload of the hammer spring.

To get useful hammer debouncing, I found that you always need to provide somewhere for the energy of the hammer's rebound to be dissipated permanently - not just temporarily stored. Springs can't do that.

Steve

 
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dan house
(Login dan_house)
Crosman Forum Member
153.90.162.47

Dissipated permanently?

June 11 2012, 12:25 PM 

and thats done thru the friction the HDD causes?

hmmm hadnt thought of it in those terms.....



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(Login pneuguy)
Crosman Forum Member
98.69.174.37

To steal Cal's word from down below: EggsActly! nt

June 11 2012, 12:32 PM 



Steve

 
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dan house
(Login dan_house)
Crosman Forum Member
153.90.162.47

hehe Guess I can go home now

June 11 2012, 12:34 PM 

got _something_ right today happy.gif

dr_subsonic's pneumatic research lab
[linked image]
the Lunatic Fringe of American Airgunning
Southwest Montana's headquarters for Airgunning Supremacy
Proud Sponsor of team_subsonic

 
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Cal
(Login CalG)
Crosman Forum Member
24.128.138.174

Moving heat from where it is not wanted is a wonderful thing

June 11 2012, 2:51 PM 

And friction can be both friend and foe.

Dragging the striker would be more effective than a spring buffer. The buffer is equal to a softer striker spring (not Eggs Actly, but close wink.gif Springs are very friction free energy storage devices.

Something compressible, but "dead" might be good...hmm Oil soaked blotter paper? leather? some material with useful elastic hysteresis?

Ideas are great!

cheers

 
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(Login curt44319)
Crosman Forum Member
69.221.167.6

Re: Moving heat from where it is not wanted is a wonderful thing

June 13 2012, 1:53 PM 

I've used with some degree of effectiveness ( and other problems ) a bit of 1/8 ID soft vinyl tubing slipped over the valve stem, and left slightly longer than the valve stem.

This does several things.
It does convert striker energy into heat, as the plastic deforms. ( on both initial and rebound strikes )
It prevents all of the striker energy from getting to the valve in the first place, hence requires a stronger hammer spring to break even. ( length is quite critical )
Being slightly long, although it doesn't suppress bounce as well as Steve's do-hicky, it does prevent the hammer from reaching the valve on re-re-bound.
It may aid in sealing the hole that the valve stem comes through, though I suspect that's about 90% wishful thinking on my part.

I'm pretty sure it works, because the no pressure dry fire boin-oin-oin-oing is replaced by
a much better ( methinks ) thwap-bump.

In any case, Steve is very right. The rebound energy must go somewhere.
Steve's devices convert a small amount to friction heat, with the balance going into recoil momentum of the entire gun. It's all dissipated.
My little tube trick mostly converts it into heat, and rebound bounce that's merely low enough in energy to not reach the valve stem for the second strike. It's all dissipated, but a greater proportion is dissipated in spring bounce and vibrations as a damped wave that's merely prevented from reaching the valve.
Steve's works with lower powered springs.
The tube trick mandates a spring much stronger than otherwise required, in order to achieve the first strike at all.
The tube trick works with the plastic breach.

 
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(Login tate308)
Crosman Forum Member
208.101.221.130

Very good answer

June 15 2012, 9:06 PM 


 
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dan house
(Login dan_house)
Crosman Forum Member
153.90.162.47

Lightening the hammer and the srping adjuster

June 11 2012, 4:17 PM 

are all discussed here and on the yellow. Search is your friend.

I'd start with "air conservation", then "hammer mods" and "spring adjuster"



dr_subsonic's pneumatic research lab
[linked image]
the Lunatic Fringe of American Airgunning
Southwest Montana's headquarters for Airgunning Supremacy
Proud Sponsor of team_subsonic

 
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Cal
(Login CalG)
Crosman Forum Member
24.128.138.174

That seems to have worked for me!

June 11 2012, 6:31 PM 

The new 392 sports a light weight striker. less than 40 grams, and a preload adjuster that allows zero preload prior to cocking.

Along with a teflon "friction collar" that fits around the striker (my own design HDD ;0!) The report on firing is much subdued and a simple Pfft where previously the sound lacked crispness.

I do need to pass some shots over the chronometer however.

A side note, this configuration Holds POI for the first shot on ten pump strokes (Oversized valve volume) and still requires FIVE shots to empty the valve.

Like I said, I need to get it over the chronometer.

cheers

edits, as some of the text regarding striker and spring seemed not to make the jump to hyperspace.

 
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dan house
(Login dan_house)
Crosman Forum Member
71.210.114.92

yea sounds like you need to be searching those your self

June 11 2012, 7:03 PM 

and on the yellow. lot of good material to learn from


dr_subsonic's pneumatic research lab
[linked image]
the Lunatic Fringe of American Airgunning
Southwest Montana's headquarters for Airgunning Supremacy
Proud Sponsor of team_subsonic

 
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(Login CalG)
Crosman Forum Member
24.128.138.174

nt

June 11 2012, 7:15 PM 


 
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(Login CalG)
Crosman Forum Member
24.128.138.174

nt

June 11 2012, 7:16 PM 


 
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(Login CalG)
Crosman Forum Member
24.128.138.174

Dan, based on your suggestion to search on Air Conservation

June 11 2012, 7:12 PM 

I did search exactly that.

I was dismayed when so many of the threads turned acrimonious.

signal lost in noise!

 
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dan house
(Login dan_house)
Crosman Forum Member
153.90.162.47

Acrimonious

June 12 2012, 8:48 AM 

yea, its not bad here on the green, but over on the Jaundiced side, things get ugly sometimes

Sahme too cuz every body here and there has soemthig to contribute

Ignore the nasty attitudes and see what yo can gleen



dr_subsonic's pneumatic research lab
[linked image]
the Lunatic Fringe of American Airgunning
Southwest Montana's headquarters for Airgunning Supremacy
Proud Sponsor of team_subsonic

 
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