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Old 02-16-2008, 11:11 PM   #11 (permalink)
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Ahh big hole in 12 gram...maybe a weak valve spring....

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Old 02-16-2008, 11:47 PM   #12 (permalink)
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try first eliminate these things

temperature play at 65F or higher
paint to barrel match must be spot on 689 or higher for size it also the consistency of size and roundness or critical
exhaust valve may be turned 90 to the port for transfer this will kill efficncy
Thank you! This is the sort of thing I was really looking for, a list of potential causes. I know this thing is going to be a beast without serious work, but 8 shots per 12gram sounds more like something actually wrong.

I'll check the valve spring, too. I imagine a stiffer valve spring would help improve efficiency, yes? We're talking huge holes in the 12gram, like, full valve stem size. Soft valve spring would definately answer why that's happening. It has the interesting side effect of making the first shot go at almost full velocity, though!
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Old 02-17-2008, 06:56 PM   #13 (permalink)
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I put a stiffer spring in the valve (actually a spare Phantom one I had lying around) and it's punching noticibly smaller holes in the cartridges. I'll have to wait 'till I can go to a field to chrono it to know if it's helping, though.
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Old 02-17-2008, 07:29 PM   #14 (permalink)
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Old 02-17-2008, 10:22 PM   #15 (permalink)
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Ha ha no.

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Old 02-22-2008, 07:37 PM   #16 (permalink)
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Okay, just got back from the field. No real noticable improvement with the valve spring swap. One thing could be that I have NO idea how stiff the valve spring should be, and that the one I put in (it's a nelson one, out of a phantom) is also way too soft. Can anyone give me any insight into this? I have to back my RVA out a whole lot to get it shooting in the 250 range, so I'm still under the impression this is a contributing factor.

Also, can anyone really explain to me how boring the valve ports/transfer port improves efficiency? I don't really see how it would. Understanding is key!
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Old 02-23-2008, 01:04 AM   #17 (permalink)
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Also, can anyone really explain to me how boring the valve ports/transfer port improves efficiency? I don't really see how it would. Understanding is key!
the main things you will do when reworking the ports is opening up some ports and closing off other ports. when the valve is put back in you will position the opened(bored) port in a manner that directs the gas flow directly into the bolt and it is a much more efficient way compared to the stock valving. you will also be opening up the port in between the barrel and lower tube.
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Old 02-25-2008, 06:30 PM   #18 (permalink)
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So that is what that grub screw under the valve was for on the hurricane... hmmmm....

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Old 02-26-2008, 02:40 AM   #19 (permalink)
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Take a look at a Cocker valve compared to a stock (or even a Turbo) PGP valve.

If you enlarge the transfer hole and the exhaust hole facing it while closing off the rest of the exhaust holes, you somewhat reduce the "volume" of the valve. A PGP valve (iirc) had 3 exhaust holes around it so orientation isn't too important. When you fire the gun, it fills all that area between the orings with CO2. A Cocker valve has only two holes, one of which (iirc) has a screw stuck in it to maintain orientation. They also don't have that skinny area "between the orings". By lessing the volume, and improving flow, you increase your efficiency.

Look at it this way. Between the back of the ball and the valve, there is so much volume. Accelerating a ball to 300 fps requires so much pressure (I've heard 60-70psi tossed around) The bigger the volume of space between the ball and valve, more gas is required to get your pressure to make 300 fps....Thus by reducing the volume, with maximum flow in mind, efficiency can be increased....(That's why the Palmer guns have the valves filled, and the valve stems turned down a little....)

You might check your bolt orings too. I imagine that it's a minor thing like the paint/barrel fit, But you never know. Sometimes if you stack a bunch of little things up it kills your efficiency before you know it.

Catchya on the Flip Side.....

Emerald Wolf -- You 12g seal isn't leaking is it?

PS -- they are pretty temp sensitive. My PMI1 will spike around 20-25fps based on whether I've been putting my hand on the tube behind the pump handle (basically on top of the 12g) Sucks when you're trying to chrono. I have to remember not to hold it right there....(Probably should go get a long pump handle for it)
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