Does powder produce more pressure in really cold temps?

[supercrossbmx69]

So I received a new custom from Kirby a couple weeks ago and things are not going as I hoped. I have been trying to develop a load using RL50. I figured to save barrel life, I would start 5 grains below Kirby's max load and work up in 1 gr increments. So I loaded up 125-130grs of rl 50, and went to the range. Temp was roughly 9 degrees according to my kestrel. 10 thou off the lands.

125-3137 fps heavy ejector
126-3187 blown primer???

Kirby believes since RL50 is such a new powder, it's possible that it produces more pressure at really low temps, which he believes would not change velocity.

But I was under the assumption that pressures REDUCE in lower temps??? Kirby's test with his 338 raptor was in 80 degree temps and he worked up to 130gr of rl50 before he felt slight bolt lift and saw a slight ejector mark which is where he called it his max.

I was fully expecting to easily reach the 3200fps mark based of Kirby's test with his test rifle which is exactly to same as mine besides I have 1" more barrel. I guess that's what I get for being the first production 338 raptor. So far I've tested RL50 and H50BMG.

 

[MudRunner2005]

I could be wrong, but I believe powder & case pressures increase when ambient temperature increases.

However, H1000 is not as temp stable as they say it is. My STW loads during the winter time are spot-on...During the summer, the accuracy goes haywire. So I have to adjust my load.

I have found that IMR 7828 SSC seems to be a nice all-weather powder, and not very finicky. Same goes for Alliant Reloder 19 & 22. For .308 based calibers Varget is always the way to go.

 

[benchracer]

I remember reading somewhere (I wish I could remember where) that double base powders can sometimes produce pressure spikes in extreme cold weather. You may wish to try a single base powder and see what happens...