imr 4064 .308 with fps verified/ theory

[armymedic.2]

My chroni is not here yet and it will be too cold to use when it gets here, so im wondering out of a 26" tube, anyone running imr 4064?

my new load is 42.2 gr out of lapua brass pushing a 178 amax.

anyone got anything close?

and if i had a load verified fps at 41.5 gr, are there any formulas to understand what the .7 gr increase gained me in mv?

thanks for lookin.