Powder temperature sensativity

[Alycidon]

In my PPC I use one powder load, 29.5gr x N133. Over this I fire 68gr Barts match bullets, 65gr Vmax and 55gr NBTs.

 

 

Playing about with it the other week the loads were chronoed as they were in March when we had another play. I did not take to much notice untill yesterday when I saw that the loads in March chronoed 100fps faster in the bigger two bullets yet about the same in the smaller one.

 

Differences are about 100fps at 3250-3300 so maybe 3%, both days were warm pleasant days. Difference must be the round temperature, maybe where I kept them prior to firing etc.

 

At the distances I shoot it wont make any odds but its an interesting observation.

 

A

[shrek]

I found my accuracy load for my 6BR in thw middle of winter, going through spring it started to open up, so i dropped the load by 0.2 gr and it braught it back onto single hole groups again. Its obvously worth a consideration when shooting at range!

[eldon]

I find my load of v140 in my 308 ok all year round but if I shoot a long string in summer the bolt gets stiff, ooh err

Never have that problem in the colder times.

[Andrew]

Powder sensitivity to temp is an interesting study. Living in the desert areas along the Mexican border I could get my 17HMR to the mid 2700's on a 125-degree (F) day. The same ammunition at -30F here near the Canadian border barely squeezes past 2400 fps. Here our weather goes through extremes so handloaders are generally careful to make up their loads in warm weather to avoid surprises.~Andrew

[eldon]

From the site I posted on reticles comes this piece which is maybe hard going in places but a good article non the less,

 

http://extremelongrange.com/images/Pressure_20Factors.pdf

 

Might answer or suggest ideas to think about. So deduced from this article not only should we be keeping the rounds covered before use in summer but also the barrel in its slip or cover to avoid heating that as well.