Chapotraphouse

Americans did have special units with rifled flintlocks. The rifles were just way more expensive to manufacture and took longer to reload as you had to jam the misketball down the barrel, fighting the rifling all the way. But they were popular with frontiersmen, and so there were rifled units that would attempt to snipe and ambush British columns. The tactic was successful enough that the British would have their own rifled units during the Napoleonic wars, most famously in the guerrilla campaigns during the peninsular war in Spain.