+1 from a former statie here. Send letter, tell chief that you have been advised that firearm has been recovered, but that it has not been returned to you despite your request. Simply state that you wish to have Smython revolver, serial number 1234 returned to you at this time- or to be advised WHY your property is being unlawfully held by HIS DEPARTMENT.
If the people your gun was recovered from are under investigation for other crimes, yes, the crime lab may want a fired casing/bullet to do a matchup- but putting the CLEO on notice increases the care that somebody will take to see that i's get dotted.
Ran across a detective a few years back that made the statement that if it was up to him, NO "civilian" would have any firearm. Smiled, told him that it was fortunate that neither he nor I got everything we wished for, since I wished that public servants that acted like fools would be fired. Took him a minute to sort that one out.