Please post your recipe!!!!!my .02 cents. I have been working up loads for a 270-4831sc and 300-H1000. in the 300. 3 different brass, and 2 different bullets (copper and lead). In all caliber and bullet combinations. My accurate load is usually .5-1 gn. less than when pressure starts appearing. And have had similar velocity losses as you. Most of my testing has been at 70-80F. One thing I haven't tested which I know may happen in the field is cooking the second round and the bullet shift after firing. I have however seen significant velocity changes end up at the same POI when using a chrono in my testing.