Need help to ID this 1840 A. WATERS handgun

[mossberg500]

Big A on the wood stock, PY in front of the trigger guard
Markings: A. WATERS MILBURY. MS. T mark on the right side next to the hammer 1840, barrel mark USLS ,
This is my friends gun im trying to help him sell this gun his dad passed away, any info thanks in advance, after I get all the info and how much it worth I will post it here for sale thanks.

[Geologyjohn]

Mossberg, I think that your buddies pistol is a Model 1836 Flintlock pistol that has been converted to percussion. These were made by Asa Waters and also Robert Johnson, between about 1836 to 1844. Yours friends was likely converted to percussion in the 1850's. I'd value it around $500. Take care, Geologyjohn

[mossberg500]

thank you so much for the info