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nelson1each

Accurate #7 temperature sensitivity affecting PF?

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Got my eye on a new chrono...I wanna be able to shoot through both at the same time to rule out the possibility of my current chrono being junk. The mystery continues till then.

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I just did some testing and from what I've seen there is a 10-15 fps average difference in hot and cold chrono readings. the one set of loads i had them down around 35-40f and the other rounds where around 75f. its not a huge difference and at least I know that its not inverse temp sensitive.  

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I noticed an increase of ~20FPS when chrono'ing on a cold day (35*) versus warmed (50*) day. 

 

This could also be variability in chrono and/or charge weight.  It's so minor that I'm not going to worry about it

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Update...on the same chrono I noticed a 15-20fps increase on and 80 degree day compared to the recent 50ish degree days.I know there are still some unknown variables yet. I did buy a new chrono and hope to get out this weekend and run the shots through both of them at the same time. 

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So got out to the range with my new chrono...don’t have it front of me so I cast remember what it was...competition electronics of something to that effect. Anyways it was 10-30fps higher every shot than the chrony one...but more to the 30fps side of things...I also have had a lot of errors and crazy readings on the old one more and more each time I use it. So I’m gonna settle on an average of 30fps off due to chrony being junk....and say that the other 15-20fps could be temp fluctuations. The best thing is the new chrono blue tooth’s to my phone and saves the data...so I’ll be able to check again when it get hot and compare data. Glad I got a new chrono 

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Did a hot - cold test with same batch of ammo today (MGJHP115-CCI500-10.7 AA7- 1.165 OAL).

20 rounds heated in truck from hot gun vs. 20 rounds at air temp (29F).

Average for hot was 11fps faster than cold. SD & ES were nearly identical between the two.

 

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On ‎12‎/‎21‎/‎2018 at 11:05 PM, Sarge said:

Any powder. I use WAC and it varies widely from jug to jug.

I have found WAC to be very temp stable, but agree with Sarge on variations from jug to jug. My load for almost a year was 7.2gr and MG 121 @ 174PF, switched to a new 8lb jug and was down to 166PF.

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I have not had that much variance with wac. 0.1gr at most from the last 5 8# jugs. 

 

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