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PostPosted: Sat Mar 18, 2017 7:27 am 
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Location: Winnipeg, Canada
I recently converted an old air master tube to 13-XX valve, breech and trigger frame.

There are differences in hammer stroke length, sear slot, and valve rear stop steps. None are insurmountable.

Just trying to make some sense out of the way the gun performs with retained air.

Current setup uses a delrin flat top piston and .22 cal 13-XX transfer port sleeve. There is an RVA on the gun with 13-XX hammer and a cut down 2100 hammer spring.

At 10 pumps with the RVA screw completely out of the gun, this is what I get over the chrony:

All shot with the Stoeger 8.6 gr field domes.


1. Lock 2nd 483.7 3rd 297.8

2. 496.7 2nd 576.9 3rd 233.0

3. 478.0 2nd 590.9 3rd 355.5

4. 476.1 2nd 589.2 3rd 359.9

5. 498.3 2nd 580.4 3rd 294.9

I think with a bit of spring balancing and hammer weight adjustments, I should be able to bring those 3 shots a lot closer together.

With the RVA in 4 turns from spring contact, I'm getting 2 shots at ten pumps.

1. 689.5 2nd no pellet

2. 694.0 2nd 297.6

3. 695.7 2nd 351.2

4. 690.9 2nd 296.1

Will stop here for a bit- posting from phone...


Edit: should have mentioned it has a 24" .177 cal 1760 bbl on it....
-D.S.

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PostPosted: Sat Mar 18, 2017 8:54 am 
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That's an amazing amount of air you are getting into that valve with ten pumps! Once you get the shots balanced out, you'll have the perfect 3 shot hunting gun!

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PostPosted: Sat Mar 18, 2017 9:28 am 
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There's more there yet.
I really have to get my desk top up and running...

With the RVA in all the way to the bottom of the adjuster nut at ten pumps there is no retained air. Upper 790's, which is very good for a pumper. 15 pumps, and it retains air again, with the RVA all the way in...

I have quite a bit of playing around to do yet...

-D.S.

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PostPosted: Sat Mar 18, 2017 10:04 am 
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You mentioned the valve stop is in a different place. Did you have to file it down to get the 13xx valve in the right place?

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PostPosted: Sat Mar 18, 2017 10:42 am 
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I have always found it is extremely difficult to get three balanced shots with retained air unless you have a much larger valve volume.... Two is not difficult at all, and I would make that your goal.... What you have built is virtually what I did in my Uber-Pumper, a 2100 tube, 1760 barrel, with 2289 valve, trigger and stock, and home made F-T-P and metal pump pivot....

Image

Here are the modified parts.... One of the difficulties is securing the front of the trigger group, as that hole would end up inside the pump.... My solution was a breech band that bolted into the sides of the trigger....

Image

Image

With a hammer spring from a 2100, I was able to achieve 769 fps at 10 pumps, 899 fps at 20 pumps, and it retained air at 30 pumps at 950 fps on the 1st shot, with 7.8 gr. JSB Express pellets.... I made a .22 cal version, with an extension in the valve to increase the volume, and the pump for a 1400, which managed 894 fps with 14.3 gr. JSB Express at 20 pumps, but realistically that was more than the gun could stand.... I also tried the extended valve and pump with the .177 barrel, and hit 991 fps at a ridiculous 30 pumps, and drove a light pellet Supersonic.... before returning the gun to a sane tune, and I still have it....

The culmination of those projects is my Uber-Carbine, a .22 cal using the 2100 pump tube, but only a 14.5" barrel from a 2289....

Image

That gun, which resides permanently as a Grouse gun in a case in my ATV, is tuned for two shots at 600 fps from 19 pumps, or one shot at 10 pumps.... You can tune a Retained Air pumper by either varying the number of shots, or varying the hammer spring preload.... Here is what happens as you change the number of pumps....

Image

The blue curves are the way I have it tuned, using a Disco spring at "normal" preload.... I also tried it maxed out, just shy of coil bind, which gave the results in red, but was simply too much pumping and too hard on the linkage (and me!).... You can achieve pretty much any crossover velocity for the two shots, by balancing the hammer spring preload against the number of pumps.... Searching this Forum should bring up the old threads....

Bob

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PostPosted: Sat Mar 18, 2017 11:48 am 
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Looks like you answered my question as well. Awesome projects!
With Doc cutting off the back end of his tube and using the front grip frame to hold valve and not notching valve as you did, looks like the valve stop is in the right place on Docs gun, am I right?

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PostPosted: Sat Mar 18, 2017 12:55 pm 
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I have not cut the rear of my tube. The valve stop dimples are in the same location on both tubes locating from the port hole. The difference is in the step cut onto the rear of the 13-XX valve. It actually locates the valve further back...I put a thin O ring over that step on the rear of the valve to keep the transfer port lined up with the hole.
I didn't utilize swept volume the way Bob did...
I think he's got quite a bit more hammer stroke by locating from the rear of the tube...

I was thinking about those 3 shots, and they are all far apart and inconsistent as well. I'll have to wait until next week to run some more numbers....

-D.S.

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PostPosted: Sat Mar 18, 2017 1:59 pm 
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My mistake!

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PostPosted: Sat Mar 18, 2017 2:01 pm 
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I thought you had done what Gipetto had suggested I do with the 760 tube. Interesting to see some pictures of what you did and how the 2100 tube differs from the 760 and 13xx.

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PostPosted: Sat Mar 18, 2017 3:29 pm 
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Moving the valve back was to get back some of the swept volume of the 2100/2200 pump that is lost by using the much longer 13XX valve instead of the very short 2100/2200 valve, which is tiny internal volume, and hurts the power potential....

Bob

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PostPosted: Sat Mar 18, 2017 3:39 pm 
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Right, I understand why you did it, great work. I just assumed the 760 tube had the same configuration on the back end as the 2100, with just a shorter pump area. I cut an inch or so off the back of my 760 tube and had to cut the sear slot longer. Everything else lined up like the 1322. Anyway I'm always assuming things and making a... (fool) of myself, lol

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PostPosted: Sat Mar 18, 2017 4:08 pm 
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Thanks for posting things like this Doc, makes for great reading and calculating what has to be done vs my own skill level...so even if I go "nope not gonna happen" I still love reading about your projects :)

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PostPosted: Sat Mar 18, 2017 8:22 pm 
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Hi Bob.

I noticed a couple of things in your photo. I see a step milled into the rear of your valve, and a 2nd port hole in the tube. I can't figure out how you got that set up to work.

I can actually see the milled step on the bottom of the valve working with the way you have located from the tube rear edge, but that 2nd port hole mystifies me.

Power would be nice, but it's not an absolute requirement for me. I have 3 pcps here should the need for velocity arise. I'm currently intrigued by 560-620 fps as that seems to be a common competition velocity in .177 cal. My meagre work over the bench rest seems to bare the truth of those velocities- up to a point. ( I still get into snits over things like having to have a 10.1" bbl .177 pistol on hand)

I have a remaining 2200 tube here that will eventually be reworked in similar fashion...

I won't get any pics up until I get home computer running again...

Edit:
Got it Bob!

The 2nd port hole is still to the rear of the valve o ring :rolleyes:

-D.S.

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PostPosted: Sat Mar 18, 2017 9:58 pm 
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Doc Sharptail wrote:
There's more there yet.
I really have to get my desk top up and running...

With the RVA in all the way to the bottom of the adjuster nut at ten pumps there is no retained air. Upper 790's, which is very good for a pumper. 15 pumps, and it retains air again, with the RVA all the way in...

I have quite a bit of playing around to do yet...

-D.S.


This is why I don't like posting from the phone. Blew it here between auto correct and typos.
Above should have read upper 690's, which is still very good for a pumper... mid 750's at 15 and retained air again.

I have a bit more preload available by taking the adjuster nut off the RVA bolt...

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PostPosted: Sat Mar 18, 2017 10:17 pm 
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I'm pretty sure that flat top valve Bob has pictured there has a shorter front end on it, looking at mine anyway looks short. I guess that wouldn't affect the port but moving it back with that notch in the back of the valve would make it necessary to drill another port hole wouldn't it?
I should keep my comments to myself, just end up showing how ignorant I am, lol.

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