It may not shoot at all
Alot of times when a ML is stored standing upright the oils in the bbl will creep downward towards the breech and it will ruin the powder
You might be looking at a disassemble the empty the contents and push the bullet out with your cleaning rod
Id wrap oooo steel wool around a bore brush and swab the bbl to clear it of any fowling and corrosion

When I need expert advice I tend to talk to myself
The older I get the better I used to be