I looked through my gun books,and it doesn't appear to be from any military musket or rifle.It is similar to many civilian rifle locks that I saw photos of.From the looks of your lock,I'd say it was never converted from flintlock as some were.Your lock would date from the 1830's,when percussion ignition was invented,until cartridge rifles made percussion temporarily obsolete.It likely dates 1830-1870.Oh,I forgot to say that I'm a metal detecting maniac!I want to find a gun very badly!So far I've found bullets and shell cases and a rifle butt plate.That lock is a GREAT find!