To the best of my knowledge there is only one American proof law, adopted in Massachusetts around 1804 (I've forgotten the exact date). The barrels were to be marked PM over the initials of the proving inspector and the date. The most common mark is that of Luke Harrington who apparently worked in Milbury where the Waters factory was located. Waters had barrel rolling machines imported from England and provided many barrels used on the generic "New England Militia Muskets." I wrote an article on the Massachusetts proof law that was published in Man at Arms in the March/April, 1985 issue.
The law was worded in such a manner that it apparently only applied to barrels made in Massachusetts. From surviving examples (at one time I had about 60 of them) barrels with federal proofs, sold as surplus from Springfield or by Federal contractors did not get the Mass. proof. Thus far I have never seen a NE rifle with such a proof and I've seen exactly one pistol...an underhammer made by the Ruggles brothers.
But...lack of proof does not prove American manufacture. The biggest source of gun parts in the Federal period was England and British law did not require the proof of export guns or parts. If it was not going to be sold at retail in England, proof was not mandatory. In fact, the British proof law of 1813 only applied to England and Wales...it wasn't extended to Scotland and Ireland until later. Prior to 1813, proof was only required in London and the surrounding Middlesex county. MOST barrels were proved because the customers expected it, not because it was the law.
