Why Can't I Get the FPS Out of My 30 cal Impact

Forums PCP Airguns PCP Airgun – Discussion Why Can't I Get the FPS Out of My 30 cal Impact

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    AirgunBill
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    I did this video of the removal again of the hammer assembly, valve adjuster and associated parts then re-install to show AGN and see if I am doing it correctly. Also to show how the hammer spring stop protrudes out 7.80mm from the cocking block face. (I may be calling some parts wrong but I hope you get the idea) Bill

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    jking
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    Bill, I don't remember mine sticking out that far, I was thinking more like 5mm. It has been a while though and I'm not 100% but visually yours looks to extend further. If that's the case I could see where yours might be limited if its bottoming out in the valve stop if it happens to be longer. Are you using the valve stop with the rubber ball or the new one that came with the PP? If I had time (heading out of town in a few hours) I'd pull mine apart and double check. Back at the magazine port does the end of the valve rod come out flush with the the magazine slot?

    Jimmy

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    ShootStr8
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    I found these — they might help.
    It's a HUMA-AIR Pellet Probe & Transfer Port modified for increased air flow.

    Could help you squeeze out a few extra ft lbs.

    No need w/ my .22 barrel, but I might try them on my .30 barrel kit when it arrives.

    EDIT:

    Found this

    • This reply was modified 5 months ago by ShootStr8.
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    AirgunBill
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    ShootStr8

    I found these — they might help.
    It's a HUMA-AIR Pellet Probe & Transfer Port modified for increased air flow.

    Could help you squeeze out a few extra ft lbs.

    No need w/ my .22 barrel, but I might try them on my .30 barrel kit when it arrives.

    EDIT:

    Found this

     

    I bought a couple of those for my 22 cal rifles and install one on my DreamPup and even opened up the one a little more with not much difference in fps. The modification SPAW did on my 30 cal. ports ( everything looks bigger on the 30 cal. ) was a complete port enlargement through both sides of the barrel port so air flow in that regard should not be an issue. Bill

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    AirgunBill
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    jking

    Bill, I don't remember mine sticking out that far, I was thinking more like 5mm. It has been a while though and I'm not 100% but visually yours looks to extend further. If that's the case I could see where yours might be limited if its bottoming out in the valve stop if it happens to be longer. Are you using the valve stop with the rubber ball or the new one that came with the PP? If I had time (heading out of town in a few hours) I'd pull mine apart and double check. Back at the magazine port does the end of the valve rod come out flush with the the magazine slot?

    Jimmy

    Jimmy I am using the Power Plenum valve stop built in to the hammer. I looked at the end of the valve and the valve was a little recessed in the valve block about 1.00mm so I moved it flush this morning and really snugged down that set screw. Even with that, which I thought might shorten up that 7.80mm protrusion of the hammer stop the measurement stayed the same. I will be going out later today to see if everything functions and I get the higher fps I am looking for. Bill

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    Chuck26287
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    I just watched your video.  When you have >7mm sticking out, and you pushed it in against the spring pressure and it stopped going in, that was when your valve was seated.  That's what causes it to stop… the valve seats, and it can go in no further.  That's when you take the measurement.  If you watch your video, it looks pretty close the ~6mm (or the 5,85mm it was before) when you push it in and the valve is seated.  When you release the finger pressure holding it in, the spring is pushing it back out to >7mm.  If the front of the rod is moving forward, so is the back end by an equal amount, so your valve is opening by the same amount the rod moved forward, and the >7mm measurement is being taken while the valve is not closed.  You want the measurement taken when you push it in until it stops (valve is then seated closed).  That doesn't look like it was very far off, since you look to be pushing it in ~2mm to seat the valve against that spring pressure.

    When you get it all back together, the valve spring should overpower that little bit of hammer spring pressure holding the valve open.  Looks like you should be fine.  Let us know!

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    AirgunBill
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    Chuck26287

    I just watched your video.  When you have >7mm sticking out, and you pushed it in against the spring pressure and it stopped going in, that was when your valve was seated.  That's what causes it to stop… the valve seats, and it can go in no further.  That's when you take the measurement.  If you watch your video, it looks pretty close the ~6mm (or the 5,85mm it was before) when you push it in and the valve is seated.  When you release the finger pressure holding it in, the spring is pushing it back out to >7mm.  If the front of the rod is moving forward, so is the back end by an equal amount, so your valve is opening by the same amount the rod moved forward, and the >7mm measurement is being taken while the valve is not closed.  You want the measurement taken when you push it in until it stops (valve is then seated closed).  That doesn't look like it was very far off, since you look to be pushing it in ~2mm to seat the valve against that spring pressure.

    When you get it all back together, the valve spring should overpower that little bit of hammer spring pressure holding the valve open.  Looks like you should be fine.  Let us know!

    Chuck I did take a measurement with it pushed in and bottomed out and I believe it was about 5.20 mm. Anyway I went out this morning and did a tune and got the fps I was looking for with the VK 50's on max power wheel at 128 bar for 870 fps with the FX Radar and 890 fps with my Chrony both set up at different times for the readings. The JSB 44.75's were going at 860 fps with the FX Radar and about the same with the Chrony. I zeroed the VK's at 50 yards and shot four pigeon's this evening at 96 yards. The 30 cal. is certainly in a different league power wise somewhat loud with the VK's and a Tanto moderator on but mouse fart quiet shooting the JSB's. Bill

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