Powder Temp v MV

[PhilM]

So a week or two back I used my Magnetospeed to chrono some of my loads.

The day was 25c air temp, and the rounds in the sun a little on top of that. The average MV was 2785 with an SD of 5.4

 

Today with an air temp of 21c, rounds from

the coolish car, I shot more of the same

batch of ammo, and recorded an average MV of 2795 with an SD of 5.4 also.

 

I was under the impression that the warmer the powder/day the higher the MV, but my results suggest otherwise on this occasion. 

 

With 10fps difference on average with an SD of 5.4, maybe this is not worth thinking about? And maybe I should think of my average MV as 2790 instead?

 

I was hoping to use the different temps to input some Powder Temp/MV data into my Kestrel 5700AB, but maybe only a 4c difference in temp is not enough anyway (I have read I should aim for 4 readings 15c apart? - fat chance in the U.K.!)

Any thoughts? Cheers!

 

[Chanonry]

If we are getting pedantic we don't really know what the inputs were (ammunition and chamber temps) to associate with the output i.e. mv measurements. We have some qualitative input data and quantitive output data but only a minor change.

So usual stuff:

How large were the sample sizes? Is the data correct but just represents a different sample from the ammunition batch. In other words are the sample sizes large enough to highlight a statistically significant change in velocity. If not then maybe you should just average the numbers. In reality it is probably not valid unless you were unusual in the shooting world and shot a really large sample. Nobody else seems to.

21 C and 25 C are not big shifts so can the velocity effects be measured accurately or are other effects interfering.  I take measurements when it is 'cold' and when it is 'hot'. You will get a more representative result. Really you want to take measurements at the high and the low, then you can be reasonably sure it is accurate between the two, the further you get outside those limits the less certain you can be it is correct?

To be really pedantic, you see some of the guys in videos from the US using a thermal temperature instrument to measure ammunition AND chamber temperature. So you would have control over the input therefore be better able to interpret the trend (or lack of).

Life is too short...

 

[No i deer]

Some powders are less temperature sensitive than others.there must be a chart somewhere on the net.i believe H4350 is the most stable

[TJC]

Applied Ballistics recommends a 30F difference in temperature readings.