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Old 05-17-2007, 02:23 AM   #1 (permalink)
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12gm secrets please

I'm hoping to set up a pump for stock class or vertical tube 12gm operation sometime soon. But I'm curious about some of the info I've seen about valve size, "packing" or devolumizing the valve area and the valve transfer hole sizes and stuff like that. Also what about the bolt itself? Would that benifit from smaller passages that suddenly step up to larger just before the ball seat?

At this point the info I learn will go towards my Pump Piranha project and towards the USP pistol that doesn't quite get 20 good shots out of it.
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Old 05-17-2007, 02:29 AM   #2 (permalink)
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I think that proper sizing of the bolt goes a long way. You often see huge bolt transfer ports these days for "high flow" and they're a load of crap. Too much expansion before the ball is no good at all.

With 12 grams, expansion is generally a no-no. That's why re-valve volume is reduced. I'm no valve expert so I won't get into those, but proper spring balancing to reduce bounce is another factor to take into consideration.
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Old 05-17-2007, 02:54 AM   #3 (permalink)
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In general, high pressure=good.

Cheap trick: put wire in the air lines to take up any extra space, which is just wasted energy. Fill any volume that isn't directly related to moving through the valve, and you may even want to fill some of that.

To my understanding, the best bet is to get an appropriate powertube #6--(.185" ID, IIRC. May be .125") is the most popular--and then try and stay as close to that internal volume as possible until right before the ball. You want *some* expansion, because a sharp jet just may jab a hole in it.

For Sheridan-style pumps, stay awa from the 'low pressure' bolts. Find the diameter of the transfer hole, and stick to that.
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Old 05-17-2007, 07:04 AM   #4 (permalink)
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Also realise that 12grams tehse days suck.

Last week I got 2 empties in a pack... barley got 2 shots out of the things, and one gave me over 10 shots in a gun that normally gets 8.
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Old 05-17-2007, 09:01 AM   #5 (permalink)
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Is it the stock valve in the USP? I've heard of people gaining shots by switching to the PMI turbo valve:
PMI Turbo Valve Review / Reviews - pbreview.com
Edit: the lower pressure requirements because of greater volume give more shots, if I've got that right?

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Old 05-17-2007, 09:32 AM   #6 (permalink)
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They may have balanced the recock jet and air going to the bolt with that valve.

(It still amazes me that no one has come out with a pistol version of the ICD 'Cats)
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Old 05-17-2007, 11:25 AM   #7 (permalink)
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Converting a PMI Piranha/USP to pump action?
Make sure you plug that blowback port on the valve first.
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Old 05-17-2007, 11:50 AM   #8 (permalink)
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Quote:
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(It still amazes me that no one has come out with a pistol version of the ICD 'Cats)
Its because Zap is sitting on the patent with its electro-cat variants (ZXS-600/800).

Aldo Perrone is a bit of a patent hog, making money through licensing. Shame, since it could make for a TINY pistol.

Nick
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Old 05-17-2007, 12:34 PM   #9 (permalink)
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just another reason for me not to like Zap...
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Old 05-17-2007, 01:15 PM   #10 (permalink)
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Quote:
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(It still amazes me that no one has come out with a pistol version of the ICD 'Cats)
I seem to remember one being marketed at one point in time. Or, it may have been a "conversion" kit. I know there was a horizontal "magazine" type feed that replaced the stock powerfeed (which is held on with a dovetail and a set screw, IIRC) which was unusually expensive due to the machining involved. I think it was done on a 6-axis CNC mill, which was apparently very costly to program and/or operate.
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