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PostPosted: Sun Apr 10, 2016 7:21 pm 
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Joined: Tue Feb 18, 2014 7:24 pm
Posts: 667
Location: Dowling ,ontario
On my .357 AR build I was stuck with a gun that was such a pain to cock that I just didn't shoot it. After a recent attempt to make a .25 pellet shooter with a Cothran power house valve ,I decided the valve was just overkill for the low power I was after.
So this left me with a valve that is super easy to open ( just breath on the stem at 3000psi ) I decided to transplant it into a qb tube.
The first step was to measure the valve and remove material from the stem side of the body so the holes will line up for the spacer/ breech screw/stock bolt block. After a few tries it ended up being .125" . You can see the misalignment in the pic before material was removed.
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Next step was to figure out how to extend the stem of the valve past the spacer block. For this I ended up using the piercing pin from the old qb valve since I would never run this on co2 . I needed to drill out the spacer block so that the flange on the piercing pin would slide into the block and have .010" clearance between it and the valve stem once butted agains each other.
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Now that the piercing pin was installed into the block the section of piercing pin needed to be cut to length , I gave it .250" past the spacer block
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Last but not least was to shorten the breech screw and stock bolt both by .125" for clearance of the piercing pin to move freely inside the spacer block.
The disco valve even though it's not a huge improvement over the existing qb does allow for way bigger porting and has a delrin valve instead of the rubber used in the qb .The QB/AR platform is better suited for a bigbore build IMO mostly due to the breech design and allows for a .5" barrel with no mods. So with this mod , I was able to retrofit a disco /Cothran valve with no other parts than the valve .

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PostPosted: Sun Apr 10, 2016 8:05 pm 
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Joined: Tue Feb 18, 2014 7:24 pm
Posts: 667
Location: Dowling ,ontario
Here are a few more pics of the swap in progress.this is a side by side of the valves
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This is to show how much shorter the stem is in comparison to the QB valve
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This one shows the piercing pin in the spacer with the screw and bolt shortened
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PostPosted: Mon Apr 11, 2016 1:00 pm 
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Joined: Wed Oct 17, 2007 3:27 am
Posts: 2586
Location: Winnipeg, Canada
Interesting...

I'm hoping that's a tube that is rated for the pressures you're discussing here. It's still going to take a bit of oomph to get those 357's up to 499-ish....

You are right about the factory QB/AR valve stems- mine pancaked around 1.4K psi. There's a work around for that though- some of our more intrepid home machinists here turn them out in delrin. The rubber transfer port seals can be easily done away with by boring a flat into the valve side, and using ice-maker tubing. I don't really see a problem with over-boring the QB/AR valves, and have done so. Bob Sterne has done a lot of work with that series, and there are some interesting photo's here.
Just a personal observation here- you'd do better, however slightly, volume wise with a disco tube. Derek Vinyard does them rated for 3K psi....

Regards,

Doc Sharptail

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PostPosted: Mon Apr 11, 2016 3:36 pm 
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Joined: Tue Feb 18, 2014 7:24 pm
Posts: 667
Location: Dowling ,ontario
Thanks Doc ,
The tube is a derrekvineyard tube rated at 3000 psi it's also 24" for lots of plenum. I've done some tuning this morning and am currently shooting the jsb 81 gr at 830 fps for 18 shots .heres a pic of the rifle.
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PostPosted: Tue Apr 12, 2016 3:41 am 
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Location: Winnipeg, Canada
That is very interesting!

Have you (ahem) de-bounced the hammer& spring?
Very impressive numbers!

I have the same tube on an A/R based build that is un-regulated, and un-bottled. It has a ways to go yet in terms of spring balancing, and de-bouncing :lol: I'm getting the occasional too heavy pre-load burp at times, and it seems to be temperature related. Mine's only in .22, and I'm seeing low 820's with a 14.3 gr pill. This particular bbl. is very fond of the JSB Heavy 18.1 gr, and I'm loping along for 17 good shots with them at mid 760's...

Glad to see a few more of the D/V tubes in actual use!

Regards,

Doc Sharptail

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