Factual error: When Benjamin is handing a store clerk some money, he is giving him a $5 bill with Abraham Lincoln on it. This happened more than 80 years before he was president. And they didn't even use dollars during the Revolutionary war. They would have used British pounds in coin form, not paper money.
Other mistake: When Martin and his younger sons attack the soldiers Gabriel sent to their camp, the body count totals 20. That includes the private who gets up and tries to run that Martin hacks to death. Later when Tavington is questioning the wounded private the Cherokee scouts brought in, he indicates he was in the fight. But Tavington states 20 soldiers were killed and the ambush shows 20 being killed. Where did the private come from?