as a class explosive, the black powder need some type of ignition source, like the fulminate of mercury going off, or the spark from a flintlock. As far as my research has told me, I've never heard of a BP rifle going off from compacting the powder with a ram rod.
The only ignition I have seen, personally, from such an action was when a spark was still present in the barrel and the powder being poured down the barrel ignited and caused the shooter some degree of pain and agony. His measure had the attached funnel which he left in the barrel. As he reached for it, the charge ignited and the measure took his little finger off.