Valentin Friedrich Langenhan had a very similar mark and was active along with his father in his shop by the mid 1840s. His firm was sourced for components for lock and set triggers and prior to WWI, possibly during, I believe Gustoff sourced them for components. His mark is an encircled "FLZ"(Friedrich(Fritz?) Langenhan Zella Sankt Blasii but I can't make your letters match.

Kind Regards,

Raimey
rse