Wow. That's a lot of powder to bring it back up from drying out. Ive been thinking about just opening up all my cans and letting them air out for a week. Then they should be good to go and I won't have to worry about it changing.I recently had a similar experience with my 338AM. Haven’t shot it in a year or 2 and I keep some powder in an old fridge in the garage that I vented. That’s where I happened to have my H50BMG, all same lot#. I live in a dry desert climate with huge temp swings through out the seasons. When I went to shoot my standard 142gr load velocity was 100 fps less than usual. I ended up bringing the charge up 3grs to 145gr now to get things back the way they were. Powder has a certain amount of moisture content and mine had no doubt dryed out somewhat. I’m bringing everything inside now where the temperature is more stable year round.
Excellent shooting and thanks for sharing. The Norma Mag IMP case is something special!
The norma improved is a awesome case. Especially now that lapua is making the brass. I have a piece with 28 warm firings on it and the primer pocket is still tight.