dont sweat it. its stable. Ive been using varget for the past 15yrs and its never showed signs of increased pressure due to heat exposure. course, ive never left the ammo box just sit and bake in the 100dg heat either, but I seroiusly dought you will either.
here in southwest texas, the winters run down to 20,s and the summers 100 plus.
you defently got some umph behind those 80,s though. i run horn. 75gr with 23.5 of varget. 75 being the heaviest i shoot.
those berger projectiles are well worth the cost if you got them deep pockets