Temperature Instability

[Grendelshooter]

Great info. Anyone have any specific load data with measured or observed effects to share? I would be interested in reading about actual changes folks have experienced.

It’s been a long time, a few years anyway, since I played with 2520 in 5.56.
Behind a 77gr SMK (trying to duplicate mk 262) it varied by more than 100fps over a 40 to 50 degree temperature range. Charges were -10% book max to .5gr over book max. I think the highest temp I recorded data at was 97*f, low was in the 40’s. Iirc low temp velocity was in the 2680’s, high temp over 2800 (2806 sticks in my mind). This out of a Douglas SPR barrel from CLE with the CLE match 5.56 chamber. Book max from Alliant was pretty gnarly during the summer, brass was done (primer pockets loose) after 2 firings. Velocity measured by a magnetospeed.
After that I moved to TAC and then 8208 in load development. Neither was consistent for me though of the three mentioned TAC was the best. It still swung pretty wildly with temp but I think it was right around 1fps/deg f. 8208 just never got me accuracy or speed, I threw a half pound of it away in frustration.
Then I found AR Comp. 23.4gr behind a 77gr Nosler CC or Hornady 75bthp in a Wylde chamber makes consistently small groups with great velocity and no real great temp instability...in my rifle anyway.