What is the age and value of a Browning sweet 16 model number 25428 with the letters FN above the numbers?

Its not a sweet 16. Sweets are a lightweight version of the 16ga. If there is no letter preceding this serial number, then you have an FN auto-5 and not a Browning Arms Co. gun. Your serial number indicates it was made in 1922, prior to the Browning Arms Co. guns. The FN stands for Fabrique Nationale which made the gun in Belgium.

You barrel should say acier special. If it does, then it was made in 1922. Value is determined by condition, but at this age, normally FN guns go around 300-500 depending on the condition.

Auto5man