How do you tell if a 1878 CC Morgan dollar is authentic?

A couple easy ways to test it are to weigh the coin and check it with a magnet. Morgan dollars weighed 26.73 grams when minted. A circulated coin will weigh slightly less, but it should still be close. Also, genuine silver dollars are non-magnetic. Fakes are made from cheap base metals. If the magnet sticks, it's fake.