I've read an early newspaper account mentioning Williams Rifled guns. Firend of mine has seen all the surviving Williams' Guns and none are rifled. It's possible there was more than one style of gun known as Williams' Guns.
There are four surviving guns that I know of and five replicas. My gun is one of the five replicas.
I have some of the Williams' family history and am putting together an account of the invention of the gun and where it was used.