ORIGINAL: Cossack
Condensation may have been a contributing factor. The gun had not been brought in overnight but was warm and exposed to the cold before coming to camp. But three 30 grain pellets are a long column and may have burned slower at 10 below.
You may be right but... Still, I like loose powder and not the pellets. I have used Pyrodex RS in my inlines in the past. But I must admit it doesn't get that cold here in southwestern Va.