Muzzle volocity change from winter to summer ?

[gixxerk8]

First time playing with subsonics in the 300 blackout SBR 10.5" 1:7 Noveske and TBAC 30p-1 at 900 asl. I developed the load in the winter which was 10.9g of 5744 under a 220 SMK and was running 1060 with a 8 fps spread. Started noticing a crack so I ran them through the chrono today at 1120 with a 9 fps spread.

Would it be normal to gain 60 fps from 40 to 80 degrees?
Would it be from the 5744, not sure on it's temperature stability?

 

[Sonic Crack]

yes. depending on the powder the fps to temp change can be very significant. Try some TrailBoss or H4198

 

[Unknown]

I have temp/velocity changes with Grendel, 300 Win mag, and 5.56. I have very minor changes with 308 because I use Varget.

Much of the change issue can be solved by changing to a powder that is less temp sensitive.

 

[gixxerk8]

Figured it was the powder, no problems with varget and retumbo. Thanks guys. 60 fps seemed like a lot.