I loaded 100gr. loose T7 on Nov 18th in my 54 cal. I left it in the unheated honey house every night and on the screened in porch when I came in for lunch. I shot it off on Dec. 22nd, worked just fine with the same primer I put in the holder on the 18th.

My BIL says he leaves his Flint lock loaded with real black. even brings it in the house at night but places a cork in the muzzle.

Do your own experimint and see what works for you.

Al