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Thread: Regulated S400 - odd POI results for 25m benchrest

  1. #16
    Knockedover is offline Strength.Determination.Merciless.Forever.
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    Out of curiosity is the cylinder floated in the stock? I've played with several 400s over the years and a slight movement has often been cured by making sure of good clearance around the cylinder.

  2. #17
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    There is some foam tape between the cylinder and stock.
    Will remove this.
    Thanks - Geoff.

  3. #18
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    Quote Originally Posted by mrgeoff View Post
    Took the barrel band off, sprayed 5 pellets across the target. I did wonder if this was good advice, with the long and seemingly very twangy barrel.

    Put the barrel band back on.

    When I last tested, I went from approx 160bar down. Today I went from approx 200.

    After about 10 shots go get zero again, I started a BR card spot on zero, then the POI dropped gradually over the first 25 pellets, and then after another 15, the POI came back up to zero....
    Next was 35 pellets POI on zero, then they started to drop again and 10 pellets later it was off the reg and dropping 2 inches on the last pellet.

    So from a full fill, maybe 90 shots which isnt bad, but a very unusual the POI dropped then came back up! If it was non-regulated, it would be the other way round!

    Everyone tells me to drop the regulator pressure down from the 125bar that Altaros recommend? Why do Altaros reccomend, and set the reg pressure at 125bar, if its not right?

    I guess I have to try it anyway, no one will let me sleep unless I do.
    Floating the barrel shouldn't cause scatter unless it's loose or something on it is loose. Try sticking some weight on the end.

    What pressure is it dropping off the reg? If it's well before it could be the reg pressure is contributing to the valve closing. Although regs supply the same amount of pressure, as their input pressure changes their response speed can change leading to different behaviour over the charge. Some valves will self regulate the speed but either the gun's recoil or the pellet in the breech is affected in a different way causing a poi change. Without changing the reg it's possible to change this but not sure of how this setup is setup.

    Walthers show a drop in poi before the reg pressure is reached, you can't see it on the chrono though. It's possible and quite easy to tune that out.

  4. #19
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    Putting the reg on a tester would show you if it's ok. You can look for creep and stability over a charge with a decent gauge.

  5. #20
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    Quote Originally Posted by Gecko View Post
    With a 120bar reg im suprissed you not getting a huge power spike as you first come of the reg, on S400 classics ive found peak pressure to be around 85bar.
    Hi,

    Bit of a late response but here goes. My S410k in .22 had peak pressure at 90 bar and a humpback whale of a power curve when I first purchased it. After a change of firing valve and springs peak pressure is now at 120 bar and curve is much, much flatter. Mine, I suspect, had the valve extrusion issue that cloverleaf talks about on this very forum.

    My four Air Arms rifles at the time had peak (i.e. very tip of the power curve arc) pressures of:-

    S410k .22 120 bar
    S410k .177 135 bar
    S410C .177 125 bar
    S400C .177 115 bar (foolishly now sold ... damn the wife)

    So I can see why Altaros set regs to 120 bar.

    Mark
    Last edited by mark112; 24-06-2016 at 01:44 PM.

  6. #21
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    Mark the peak pressure with a reg fitted will be totaly different, a S400 with a reg set to 120bar with the transfer port open when dropping of the reg the gun will more then likerly become FAC.

    Even my little 177 BSA ultra with a short 12" barrel has the reg set to 95bar, a regged S400 classic in .22 the peak pressure must be lower then 85bar judging from my eperience of regging 177`s.

  7. #22
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    So difficult to work out good advice, sorry to all, I just can't work it out.

    I cronnyd the rifle, it's MAXimum output was 11ftlbs, with a full fill.
    The power drops approx 0.2fbs just before it rolls off the reg. At this point power drops like a stone. The transfer port is fully open. Think I have said all this before.

    If I drop my reg pressure, I will simply have to have less pre-load on the firing pot Spring to up the power again.

    What actual physics are going on with the rifle to make the poi shift when the reg is fully in, the chronnyed TPS show a gradual drop from full to just off reg, the manometer is around 125bar the entire time.

    Maybe it's mechanical, maybe it's the reg, I just can't work it out, trial and error I gues!
    Thanks - Geoff.

  8. #23
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    Which reg is it, the one that replaces the firing pot i.e the reg screws into the firing pot?
    Though even the newer one doesnt require a breath hole, with out stripping one it appears a stange design.

  9. #24
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    Try preloading the spring and upping the hammer.

    To me either the reg isn't flowing as fast when the input pressure drops or the reg isn't delivering consistent pressure as it drops.

    If the valve is being assisted by the pressure and flow from the reg, and the reg delivery changes the valve has less resistance which makes it open longer and or bounce more, normally meaning it feels blatty. If you preload the return spring it becomes less reliant on the reg and susceptible to its variation (in my experience). For the sacrifice of a little more hammer this should translate into more efficiency.

    I think reg pressure is a bit of a red herring. It's the effect of high reg pressure and high flow which has the impact.

    Ideally though you need a reg tester for it. For all you know the reg could be at fault. But I think it's an assumption that regs solve all... Unless the rest of the system is set to accommodate it then it may not.

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