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392 carbine progress update

June 14 2012 at 1:42 PM

  (Login Dnadnnoid)
Crosman Forum Member
from IP address 98.232.166.154

i cut the new slot and drilled holes for the tube plug. I didn't realize i would need to cut the slot so long to accomodate the original pump arm. i ended up losing alot of stroke volume. i think i'll have to just make a new valve using phil's idea and turn it into a SSP. as it is now with the reduced volume in the valve and about 3 inches (approximately) of air per stroke, it shoots a 14.3g cphp at 530 fps on ten pumps...

im still waiting on the guy at the machine shop to finish the 7/16th sleeve that will fit over the end of the barrel

here's some pics of it:

the bottom gun is my 397 for comparison

[IMG][linked image][/IMG]

[IMG][linked image][/IMG]

[IMG][linked image][/IMG]

DNADNNOID


    
This message has been edited by Dnadnnoid from IP address 98.232.166.154 on May 7, 2013 4:29 PM


 
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dan house
(Login dan_house)
Crosman Forum Member
153.90.162.47

Sometimes you gotta build a couple

June 14 2012, 1:53 PM 

to get it the way it shows up in yer brain.....

thats looks a w h o l e lot better than I thought it would when you described it earlier.... 

Short and handy. you may be on to something with that



dr_subsonic's pneumatic research lab
[linked image]
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Southwest Montana's headquarters for Airgunning Supremacy
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(Login Dnadnnoid)
Crosman Forum Member
98.232.166.154

ha, i didnt have a lot of faith i could make it look that good either

June 14 2012, 2:03 PM 

i took my time. spent days and sleepless nights thinking about it before doing anything

the length really is perfect i think. however it will be just as long as the original once i put a muzzle brake on it

once this is all the way finished im going to buy a refurb and start again.

in the mean time i'll be doing some thinking about what to do about the lever

 
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(Login robnewyork)
Crosman Forum Member
166.248.7.228

how will u hollow the stock?

June 14 2012, 4:37 PM 



[linked image]
"i never was much for book learnin"

 
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Phil
(Login Duane30)
Crosman Forum Member
74.140.194.8

Hey, Trev. Fun, isn't it!?

June 14 2012, 2:40 PM 

Nice work.

If you ar concerned about the stroke, purchase a Benji HB pistol inlet valve. It is shorter in length AND has much less volume. You would see gains immediatley on 10 pumps. However, you will then need to add some length to the factory piston (slightly less than 1/2"). To do this, (1) you can cut the piston rod then thread both ends (1/4x20 threads) or, (2) heat up the end where the lever link attaches and pull out the piston rod and thread the hole to 1/4x20 thread and the piston rod. You then would need to use a sleeve nut to capture both ends.

As far as the slot. The slot should have needed to be extended the same amount that has been removed from the tube, (edit) that's if you were using factory components. I did not scroll far enough to see the piston unitl later - oops. Put a rod in that piston (make it longer), problem/stroke will be solved.

Survival Benji? Now time to bed liner the stock.

"The majority of things in our lives are created by folks no smarter than the rest. Afterall, the world is comprised, and operated by C average people intellctually, academically, and morally. These people are often the great pioneers that set the precedent for what excellence should be."


    
This message has been edited by Duane30 from IP address 74.140.194.8 on Jun 14, 2012 2:44 PM


 
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(Login Dnadnnoid)
Crosman Forum Member
98.232.166.154

the piston is already adjustable

June 14 2012, 2:52 PM 

i cut it down shorter and its secured with set screws now and makes it easy to adjust through the slot. you can see it in the picture

i think i will order the HB valve. it'd be easier. I looked up your ssp valve and how you made it. im just like: huh?

 
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(Login Duane30)
Crosman Forum Member
74.140.194.8

Well, the SSP valve only uses the rear valve portion...

June 14 2012, 3:12 PM 

...The exhaust end. The HB valve has plenty of meat in the space between check seal and inlet hole to remove about 3/4" or more, which will gove more stroke room while using the same volume as an HB valve. The finished 397 uses an HB valve that has been reduced even further in volume.

The geometry of lever link length and piston length to slot have to work. Judging by what you have already, a longer piston will give more swept volume when you put a shorter valve in.

Have you calculated the swept volume per stroke?

"The majority of things in our lives are created by folks no smarter than the rest. Afterall, the world is comprised, and operated by C average people intellctually, academically, and morally. These people are often the great pioneers that set the precedent for what excellence should be."

 
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(Login robnewyork)
Crosman Forum Member
166.248.14.164

bed liner may save your life

June 14 2012, 5:04 PM 

Lol..mentioned that in previous thread

[linked image]
"i never was much for book learnin"

 
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airgunandy
(Login airgunandy)
Crosman Forum Member
206.208.93.60

I like it!

June 14 2012, 2:47 PM 

Looks about the size of the old Crosman 101/102 series rifles. Very handy little rifles. If you could get another 100 fps out of it you'd be right in the ballpark with them. Keep up the good work!

I plink, therefore I am.

 
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(Login robnewyork)
Crosman Forum Member
166.248.7.228

very cool..would 177 be more practical for woods surviving?

June 14 2012, 4:34 PM 



[linked image]
"i never was much for book learnin"

 
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dan house
(Login dan_house)
Crosman Forum Member
153.90.162.47

yes and no

June 14 2012, 5:00 PM 

if your a good shot, probably no difference

bigger game might be taken easier with bigger pellets, smaller pels means you can carry more pellets

 



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 robnewyork)
Crosman Forum Member
166.248.14.164

easier to store 177 weight and volume wise..butt not as much smack.nt

June 14 2012, 5:05 PM 



[linked image]
"i never was much for book learnin"

 
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(Login pneuguy)
Crosman Forum Member
98.69.198.150

Very cute, Trevor - but about SSP mode and stroke volume.

June 14 2012, 10:33 PM 

With the greatly reduced stroke length you've gone with, you'll probably be disappointed with the power that will result if you convert the gun to SSP. Since your pump now moves less than half as much air per stroke than stock, you'd probably find it will also produce less than half as much power as Phil's if redone as an SSP. Maybe much less.

Better stick with the MSP format so you can at least make up for the short stroke by pumping more.

Steve


    
This message has been edited by pneuguy from IP address 98.69.198.150 on Jun 14, 2012 10:34 PM


 
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