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<blockquote data-quote="SDMF" data-source="post: 364313" data-attributes="member: 412">Regarding shortening the screens, I was talking about the ubiquitous &quot;Crony&quot; chronos that fold in half.As to the pictured chronograph, it's possible to shorten the distance between the screens if the rifle and the chrono aren't both level.&nbsp; The pictured chrono times the bullet between the sensors.&nbsp; Obviously that time is extremely short, if the rifle and the chrono aren't in the same plane you're shortening the distance between the screens and thereby the bullet spends less time between these screens producing a falsely higher velocity.Differing light conditions too can change chrono readings.&nbsp; When I used an optical chronograph, I preferred to do my testing in that 1st 30min of light before the sun has actually risen.&nbsp; I liked to shoot from E to W with the rising sun behind me to illuminate the target.The radar I use now is supposedly not effective over 4K FPS, I don't have anything going that fast, I only know the instructions say it won't work.&nbsp; If I were trying to develop loads going that fast and wanted accurate measurements I'd be looking into magneto speed or a 3-screen Oheler.&nbsp; Or, I'd have some bubble levels and probably something like un-chalked chalk-line string to make sure I was shooting straight through the chrono on the proper plane.Buddy and I set up 2 fold-in-half Chrony machines in succession of each other.&nbsp; It took a LOT of fiddling to get them to correlate with each other like they should.&nbsp; It was EASY to manipulate them for an improper read once you first got it right.&nbsp; Add a little pitch either way, you shorten the distance between screens and velocity &quot;goes up&quot;.&nbsp; Level things back out and add a little yaw increasing the distance between screens by shooting diagonally across them and the velocity goes down.</blockquote>

[QUOTE="SDMF, post: 364313, member: 412"] Regarding shortening the screens, I was talking about the ubiquitous "Crony" chronos that fold in half. As to the pictured chronograph, it's possible to shorten the distance between the screens if the rifle and the chrono aren't both level. The pictured chrono times the bullet between the sensors. Obviously that time is extremely short, if the rifle and the chrono aren't in the same plane you're shortening the distance between the screens and thereby the bullet spends less time between these screens producing a falsely higher velocity. Differing light conditions too can change chrono readings. When I used an optical chronograph, I preferred to do my testing in that 1st 30min of light before the sun has actually risen. I liked to shoot from E to W with the rising sun behind me to illuminate the target. The radar I use now is supposedly not effective over 4K FPS, I don't have anything going that fast, I only know the instructions say it won't work. If I were trying to develop loads going that fast and wanted accurate measurements I'd be looking into magneto speed or a 3-screen Oheler. Or, I'd have some bubble levels and probably something like un-chalked chalk-line string to make sure I was shooting straight through the chrono on the proper plane. Buddy and I set up 2 fold-in-half Chrony machines in succession of each other. It took a LOT of fiddling to get them to correlate with each other like they should. It was EASY to manipulate them for an improper read once you first got it right. Add a little pitch either way, you shorten the distance between screens and velocity "goes up". Level things back out and add a little yaw increasing the distance between screens by shooting diagonally across them and the velocity goes down. [/QUOTE]

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