I've never heard of the standard US musket load being 150 grains. That's a huge amount of powder and doesn't seem to match up to the original arsenal loaded .69 caliber cartridges I've seen in museums and collections.
I know I read somewhere that the "original" charges were 150 with a one ounce ball but I cant find it online. I did find charges listed at 110 grains. By the time of the CW everything was standardized. Remember also that the first musket manufactured at Springfield was the 1795 and was a pretty close copy of the Charleville. At the time of the CW they were 1840's with some 16's being converted.