GTA
All Springer/NP/PCP Air Gun Discussion General => American/U.S. Air Gun Gates => Crosman-Benjamin Air Gun Gate => Topic started by: Tack Driver 10 on January 19, 2019, 06:39:30 PM
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Following in the footsteps of the crazy, incredible, unbelievably awesome 760 SHO.
I decided that since my test gun is now unemployed, why not make an honest gun of it with a FT version of the balanced valve.
The word on the street is a FT setup should yield more power so we'll see.
The 760 SHO sports a custom polyurethane cup piston and balanced valve.
This valve will be made from an old school brass valve, sorry, no aluminum allowed.
In order to make room for the balance chamber, (aka thimble) I machined the front part of the valve up as far as space would allow.
Cut a new gland and machined the center section that will support the thimble.
The thimble and throat will have the same specs as the 760 SHO, .210" x .225".
This could get hairy!
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It has been said that when one fails to plan, one plans to fail.
Failure is not an option.....LOL
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Ron,
Failure is not an option, you must succeed :D Realy nice looking brass machined valve parts. ;)
I am curious to see the fpe from the 13XX platform that you can achieve :P with 10 pumps.
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Made the valve stem from brass with a Teflon seal.
Tried a Delrin stem but it's too hard and won't seal well.
The valve spring is only 3 pounds so it needs a softer material like Teflon to seal.
Also made a new FT piston.
Duro 90 poly seals on the piston and valve.
Using a 10 gram Delrin with a 2400 hammer spring.
Bored the bottom part of the valve to .450" and back .050".
Opened the valve port to .157", ported it and cut a new seat.
The orange poly bumper limits the stem travel to .125".
Assembled the gun with an 18" barrel in 22 cal.
Just started to rain as I went to chrony it but got it done (like a true champion....LOL).
With CPHP 14.3:
10 pumps 596 FPS 11.28 FPE
15 pumps 702 FPS 15.65 FPE
I'm going to try another velocity test with a longer barrel.
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I have a confession to make:
Forgive me Forum, for I have sinned.
In my previous test I dialed in moderately high cam over.
Today I backed off the piston 1/8 of a turn and ran it over the chrony.
This would be more like an everyday setup.
With CPHP 14.3:
10 pumps 590 FPS 11.05 FPE
15 pumps 693 FPS 15.25 FPE
Only lost 6-10 FPS so no biggy.
Since the gun was still making strong power from 10-15 pumps I tried 17 pumps.
17 Pumps 728 FPS 16.83 FPE
In the morning I may go totally crazy and try 20 pumps.
I hope you all can find it in your heart to forgive me for my sins against air guns.....LOL
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You’ve got it smoking for sure! How long is the other bbl. you were going to test?
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Good work! Just sitting quiet and eating my popcorn watching your builds.
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Good work! Just sitting quiet and eating my popcorn watching your builds.
Me too! ;D
VERY nice work
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Super!!! That's hunting power there :D you sure did a fine job on that valve.
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That is SUPERB work on that valve!! Great work!!
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You’ve got it smoking for sure! How long is the other bbl. you were going to test?
I have a 22" barrel blank but made a quick 4" barrel simulator out of Delrin.
It press fits on the end. Got 15 more FPS with it.
In the meantime I pumped the 13xx SHO like I stole it.....LOL
First gave it a 10 pump warm up, then cut to the chase with 20 pumps.
18" Crosman barrel with 14.3 CPHPs
10 pumps 596 FPS 11.28 FPE
20 pumps 759 FPS 18.29 FPE (with some retained air)
Need to increase the 10 gram hammer weight.
Looks to be topping off as from 17 to 20 pumps made 10 FPS/pump.
With a longer barrel should make 775 FPS or so.
I'm good with that.
Update:
Put the 4" barrel simulator on the gun and pumped it 20 times.
20 pumps 775 FPS 19.07 FPE
Had to go there and glad I did.
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Good work! Just sitting quiet and eating my popcorn watching your builds.
and it's quite the show.... wow
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I did a lot of work on 13XX/2289 pumpers before I got into PCPs.... I still have two, a .177 cal with a 24" barrel and a .22 cal carbine with a 14" barrel.... They both use the pump tube and linkage assembly from a 2200, which has about a 50% increase in swept volume, and hence requires about 2/3 of the number of strokes for the same velocity.... Here is the rifle version....
(http://i378.photobucket.com/albums/oo221/rsterne/Uber-Carbine/Uber-PumperwithScope.jpg) (http://s378.photobucket.com/user/rsterne/media/Uber-Carbine/Uber-PumperwithScope.jpg.html)
and here is the carbine.... and the parts I made to do the job.... I later replaced the Delrin fork with a more rigid aluminum one....
(http://i378.photobucket.com/albums/oo221/rsterne/Uber-Carbine/Uber-CarbineEmail.jpg) (http://s378.photobucket.com/user/rsterne/media/Uber-Carbine/Uber-CarbineEmail.jpg.html)
(http://i378.photobucket.com/albums/oo221/rsterne/Uber-Carbine/Uber-CarbineParts.jpg) (http://s378.photobucket.com/user/rsterne/media/Uber-Carbine/Uber-CarbineParts.jpg.html)
The trigger was held in place by a breech band, as the front trigger screw hole would have been in the pump section of the longer tube....
(http://i378.photobucket.com/albums/oo221/rsterne/Uber-Carbine/Uber-CarbineTrigger.jpg) (http://s378.photobucket.com/user/rsterne/media/Uber-Carbine/Uber-CarbineTrigger.jpg.html)
I also built a .22 cal with a 24" barrel with the tube and pump assembly from a 1400 (2X the swept volume of a 13XX).... I sold that years ago.... Silly power and too hard to pump....
(http://i378.photobucket.com/albums/oo221/rsterne/22%20Uber-Pumper/22Uber-Pumper.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20Uber-Pumper/22Uber-Pumper.jpg.html)
The carbine is currently tuned to shoot two equal shots without repumping, as per where the blue curves cross over below....
(http://i378.photobucket.com/albums/oo221/rsterne/Uber-Carbine/Uber-CarbineVelocities.jpg) (http://s378.photobucket.com/user/rsterne/media/Uber-Carbine/Uber-CarbineVelocities.jpg.html)
The red curves indicate what can be done with a stiffer hammer spring and a ridiculous number of pumps.... It peaked at 770 fps (19 FPE) at 24 pumps (equivalent to 36 pumps with a 13XX pump)…. Using the gun in that way for any length of time would have reduced it's life significantly as the loads on the pump and pivots are extremely high.... A balanced valve sure would have made the gun a LOT easier to cock.... ::)
Sorry to hijack your thread, I just thought you might like to see some of this.... :-[
Bob
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Bob,
No problem, I hijacked your balanced valve thread before this thread so now we're even......LOL
Your gun was the inspiration for my 1321 gun.
A 22 cal 2100 based 13xx chassis gun.
Has a real small valve but made 757 FPS with 15 pumps.
https://www.tapatalk.com/groups/thegreencrosmanforum/my-new-1321-t47758.html#p297907 (https://www.tapatalk.com/groups/thegreencrosmanforum/my-new-1321-t47758.html#p297907)
I linked to your gun on the bottom of the last page.
I may make a 22 cal gun from a 3/4" ID tube using the balanced FT valve.
Made one awhile ago from an MK tube/766 link and it got 915 FPS with 20 pumps with a 4" stroke.
Started to retain air at the high end, won't be a problem with the BV.
The new version would have a 4 3/4" stroke.
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775 FPS. With the extra 4”....Wow!
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There's a song that goes something like this:
If you like your air gun then put a round shiny thing on it.
Good advice, so that's what I did.....LOL
I figured with 20 pumps the pressure in the valve should be approaching 3000 PSI.
I put the gauge on the gun and will run some tests in the morning.
Gave it a few pumps to see if it'll hold pressure overnight.
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"If you like your air gun then put"
I would finish this with, More into it.
And I want to, but I didn't see enough
about the "balanced valve" or a link to something.
I don't understand it and want to.
I also want to try a 13XX type build using two or three stock sized,
air tubes side by side all hooked up to pump at the same time feeding
the center valve and then only needing to have one hammer to release it.
I know if my thoughts would just stay in my head, but sometimes they get away
and is never good for stuff I wish to finish.
just
sayn
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It will be interesting to see what you measure.... Here is a thread on what I found with 3 different style piston heads....
https://www.gatewaytoairguns.org/GTA/index.php?topic=77463.0 (https://www.gatewaytoairguns.org/GTA/index.php?topic=77463.0)
Stock 13XX pump linkage and valve volume.... just changed the piston heads....
Bob
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Nice work on the project. The balanced valve concept is interesting. At 3000 psi without the balanced valve the gun would probably encounter some degree of valve lock.
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Ran a pressure test run in 5 pump increments:
05 pumps 550 psi
10 pumps 1250 psi
15 pumps 1900 psi
20 pumps 2450 psi
The 760 SHO has a similar valve but a spacer reduces the volume some, peaks at 15 pumps vs 20 for this gun.
I can decrease the valve volume and have it build pressure faster but I'll leave it be for now.
Might have to try a maximum smoke run just because I can....LOL
The pump arm is the weak link on these guns, fortunately they're only $4 a copy.
A 2100 tube with a NOS 766 pump arm and balanced valve would be ideal.
Made a 26 gram hammer from Delrin with a 1/2"x20 threaded insert machined from a bolt.
I'm calling it my hard core hammer.
Update:
Tossing caution to the wind, I pumped the gun to 3000 psi.
I pumped the gun like I stole it, then someone stole it from me, then I stole it back from them....LOL
It took 27 pumps and dumped the full charge using the 2300 hammer spring/26 gram hard core hammer combo.
With an 18" Crosman barrel and 14.3 CPHPs:
27 pumps 821 FPS 21.4 FPE
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With an 18" Crosman barrel and 14.3 CPHPs:
27 pumps 821 FPS 21.4 FPE
Hey now that's pretty respectable! ;D Is it still just as accurate?
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With an 18" Crosman barrel and 14.3 CPHPs:
27 pumps 821 FPS 21.4 FPE
Hey now that's pretty respectable! ;D Is it still just as accurate?
The objective was to test the balanced valve for power so I didn't perform an accuracy test.
I wanted to see how much power I could achieve and how much could be released without a heavy hammer/spring.
Pumping this gun 27 times is unrealistic for everyday use but was an interesting experiment, good thing I carbo loaded the day before....LOL.
Now I'm contemplating a 2100/2200 tube based 13xx gun with a longer pump tube to accommodate a full size balanced valve.
Also a 3/4" ID tube with a 4 3/4" stroke and balanced valve.