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Angle Of Sun And Chrono Readings

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Sanity check...can the angle of the sun cause errant chrono readings? I got consistently low readings today from my 9mm major load (159 PF) that usually is around 170 PF in the summer. Temp was probably around 60 degrees today, so not too cold. I know temperature can influence the powder burn, but the ammo was taken from a heated environment and not exposed to the cool air for more than 15 minutes before shooting over the chrono. The sun was coming in at about a 45 degree angle, straight into the front of the chrono. Sky screens were used as there were no clouds. I would have liked to have tried taking readings with the chrono perpendicular to the sun, but there was no other choice at this range. I'll have to try and find an opportunity to take a new reading at a different range sometime this winter. Could the angle of sunlight have caused lower than normal readings or is temperature a more likely culprit? Powder was HS-6. I'd hate to have to bump up the charge if I don't have to. Last July, I chrono'd the same load at 172 PF average out of a 10 shot group. I checked this load several times last year (albeit in warmer months) and my lowest reading on record is 168 PF.

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The Crono timer uses a sensor that reads the (shadow) of the bullet going over head, & The corno reads the time dif /div by the scoren seperation x feet per second ,etc. etc.

The sensor is no more than a shadow reading device = mess with shadows late in the day and it changes.

The time from one screan to the next is div by the screan seperation/= shadow seperation.

If the bullet is not throwing a consistent shadow the data will not be corect.

As all a box will do is controll the sadows.

You could use a arrow or broom handel to hold over the screans to see what the shadow is doing in regard to the bullets path even the highth of bullets path could effect it some

If the bullet passes 12" over the front screen and 9" over the back one that will efect the sadow too unless the shadow is thown directly down. = not likely late in the day or in the winter soltice.

BUT I may not know nothing


Edited by AlamoShooter
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I built a cardboard chrono box. Translucent plastic on top. Keep direct light off the sensors.

Good idea. I usually use a no-shoot target on top in summer to keep the sun overhead off, but that wouldn't have helped today with the angle of the sun.

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''Sometimes you need to turn sensors on their sides. "

I had to do that last week and was wondering if it made a difference.

I was testing several new .223 loads, late in the day, tipped the screens at about a 45 degree angle. I don't have the info sitting in front of me right now, but everything was consistent with the book and prior recipes.

Tipping the screens didn't seem to make a difference in my case. So, all else being equal, does tipping the screens make a difference or not??

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