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  1. #11
    User
    Join Date
    Jul 2013
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    45
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    895

    Default Re: Skyscreen blown off

    If your muzzle blast took the skyscreens off, your chrony is too close.

    Muzzle blast can cause the chrony to move, affecting accuracy of the measurement. Doesnt help to chrony loads, but you cant trust the results!

  2. #12
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    Aug 2011
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    Virtutopia
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    Default Re: Skyscreen blown off

    Agree with the guys, chrony probably too close. Try it at 6m.

  3. #13
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    Join Date
    Jun 2015
    Location
    Cape Town
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    286

    Default Re: Skyscreen blown off

    Thanks all for observations.

  4. #14
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    Nov 2014
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    Garden Route
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    53
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    755

    Default Re: Skyscreen blown off

    It shouldn't matter how far the chrony is from the rifle, it will still read the velocity. You can always adjust the reading by a few ft/sec with respect to the distance from the rifle. I imagine with 102g that must be quite a blast, so moving it back won't do much harm, as I'm sure the suggested distance is a gestimate based on most medium bore rifles. Just don't shoot the chrony.

  5. #15
    Banned
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    Dec 2009
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    Vereeniging
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    70
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    5,782

    Default Re: Skyscreen blown off

    The problem with a chrony to close to the muzzle is just not the physical affect on the chrony itself, but that the fast moving gas also triggers the sensors and you then get false readings. Five to six meters is then a practical distance to still be able to see the display and avoid the gases.

  6. #16
    User
    Join Date
    Jun 2015
    Location
    Cape Town
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    286

    Default Re: Skyscreen blown off

    Follow up on this. Took another batch of loads down to the range to start shooting for groups. Set the Chrony up at max dist that cable and range allowed which was 3.5m muzzle to unit. Adjusted so Chrony was square and level by eye and set with short length of the skyscreen arms in the unit, ie brass ferrules around 5 inch above unit, Used the crosshair on the brass ferrule of the skyscreen arm to get all shots passing over the unit at same height.

    Nine shots from the 416 Rigby (also had some stuff to sort out with another rifle which would be food for another thread some time) clocked max 2743 fps and min 2714 fps, so looks like a pretty decent set of readings without any technical issues. Probably throttle back to just under 2700 fps for a regular load.

    Thanks to all for previous comments and advice.

  7. #17
    User
    Join Date
    Oct 2012
    Location
    Noord van die biltong gordyn.
    Age
    56
    Posts
    9,116

    Default Re: Skyscreen blown off

    The 416 Rigby case has about the same capacity as the 416 Weatherby. If the rifle can take the pressure and bolt trust, you could theoretically load it to Weatherby pressure levels. I would, however, not do it!

    Also keep in mind that the muzzle blast can affect the chrono readings. At 3,5m, you are still pretty close considering the 416's muzzle blast.

    A longer cable, or reading the display trough a scope, could help to get the chrono out of the blast zone.

  8. #18

    Default Re: Skyscreen blown off

    I just put the screen on the ground or something, minimum 5m.

    Look a bit when you shoot what shockwave gets exerted on the hanging cable at 5m.

  9. #19
    Banned
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    Aug 2010
    Location
    Port Elizabeth
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    55
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    11,588

    Default Re: Skyscreen blown off

    Shooting 50 gr's of propellant through a .270 with chroni at 2/3 m often results in false readings and chroni being blasted visibly. I battled for years until Driepoot set me right ( seldom spoken -solid advice Driepoot). My chroni now stands at 4 - 5 m for my rifles, I would imagine 90+ grains would need a lot more space than 50 gr.

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