I did a google search on Niesto and it took me to several Polish language sites likely a place name. Site unseen I don't know but I suspect what you have is a Prussian model 1809 72 cal Musket Converted from flint by I don't know but the one I'm looking at has 3 brass bands a brass trigger guard and brass swivels on the middle band and on the front of the trigger guard. Does not appear to have a bayonet lug
Seems these arms were not highly reguarded by the troops. Found a pic in Echos of Glory Arms & Equipment of the Union.
Time Life 1991