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  1. #1
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    Default Skyscreen blown off

    So I recently collected my 416 Rigby and started doing load development for some 330gr GS customs. This weekend I took the five incremental charges down to the range to chronograph. I was looking for 2700fps and started with 96gr S365, by round two I had 2692fps, no signs of pressure so I fired round three which clocked 2787fps. Carefull check of case and primer, no sticky extraction so decided to fire round four, 102gr, this one clocked 2907fps, but blew the skyscreens of the Chrony clean off their supports. Chrony was about 4m from the bench. Any idea what would have caused this, muzzle blast or unburnt powder maybe?

    I wondered if I may have pulled it and nicked something, but a careful check showed no damage and the screens re-assembled normally so it was not a hit. As a matter of interest a check of the case and primer showed no signs of excess pressure but I decided not to try round five.

    Anyone have a similar experience?

  2. #2
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    Default Re: Skyscreen blown off

    Barrel length?

  3. #3
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    Default Re: Skyscreen blown off

    Shjo a flat shooting dangerous game rifle!

    Sent from my SM-G930F using Tapatalk

  4. #4
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    Default Re: Skyscreen blown off

    Quote Originally Posted by Messor View Post
    Barrel length?
    24 inch

  5. #5
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    Default Re: Skyscreen blown off

    Quote Originally Posted by SteveFW View Post
    24 inch
    Then at 2900ft/s you are what, 20 000 PSI over max pressure?

  6. #6
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    Default Re: Skyscreen blown off

    Quote Originally Posted by Messor View Post
    Then at 2900ft/s you are what, 20 000 PSI over max pressure?
    Max pressure is 47 137 Psi.
    Working up from a safe start in 2gr increments I would be very surprised to pass the max allowed pressure by 50% without any sign of primer flattening or difficult extraction. But I am doing this empirically rather than by calculation.

  7. #7
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    Default Re: Skyscreen blown off

    Quote Originally Posted by SteveFW View Post
    Max pressure is 47 137 Psi.
    Working up from a safe start in 2gr increments I would be very surprised to pass the max allowed pressure by 50% without any sign of primer flattening or difficult extraction. But I am doing this empirically rather than by calculation.
    At 2900ft/s you are close to 70 000 PSI

    But that is not so.

    Your chrony is too close.

  8. #8
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    Default Re: Skyscreen blown off

    Quote Originally Posted by Messor View Post
    At 2900ft/s you are close to 70 000 PSI

    But that is not so.

    Your chrony is too close.
    Chrony recommended setup, 3-4.5m, so could shift out .5m or so.
    Other GS Custom users have loaded 330grHV's to speed of 3100fps before finding signs of pressure, is this not a function of smaller bearing surface on the GS HV bullets allowing higher speed at lower pressures?

    I would expect to find flattening of primers, imprinting of the case head and/or binding of the bolt well before max pressure was reached. I have quickly picked up these signs on my 7mm RM when some case volumes varied in a batch.

  9. #9

    Default Re: Skyscreen blown off

    So the normal Chrony manual says 15Feet from barrel. So 4m should be fine as long as its from the tip of the barrel. And not from where your sitting.
    Also you have to shoot 4inches(10cm) above the chrony sensors. Ive seen most people try and shoot just above. And eventually sending their Chronies to Chrony heaven.

    Mark on the sunshade arms as they instruct in manual some insulation tape at the lowest point 4inches and highest point 6inches.
    Do this on front and back posts. This will also help you level the Chrony and not allow for changes when setting up again.
    I also stuck a small piece of Insulation tape on front middle. And at 5inches. So I just line crosshairs on the middle tape and 5inch level and shoot.

    You were either to close to the Chrony. Or shooting too low over it.

  10. #10
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    Default Re: Skyscreen blown off

    Quote Originally Posted by shooty View Post
    So the normal Chrony manual says 15Feet from barrel. So 4m should be fine as long as its from the tip of the barrel. And not from where your sitting.
    Also you have to shoot 4inches(10cm) above the chrony sensors. Ive seen most people try and shoot just above. And eventually sending their Chronies to Chrony heaven.

    Mark on the sunshade arms as they instruct in manual some insulation tape at the lowest point 4inches and highest point 6inches.
    Do this on front and back posts. This will also help you level the Chrony and not allow for changes when setting up again.
    I also stuck a small piece of Insulation tape on front middle. And at 5inches. So I just line crosshairs on the middle tape and 5inch level and shoot.

    You were either to close to the Chrony. Or shooting too low over it.
    Was shooting open sights but aligned to shoot over unit level with the brass ferrules on the skyscreen arms, may have been slightly high. It was shot of a bench so shots were reasonably repeatable. Seems like I will repeat the exercise and be more specific with my measurements but given no pressure signs will work with similar loads.

    Still don't know what took the skyscreens off.

    Thanks for comments.

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