Send me the shotgun, include 500 rounds of Winchester AA ammo and a brand new $50 bill (or a dirty old $100), and I will take care of the problem for you. If you would like the shotgun returned to you, please include another $50 for shipping and handling (trust me, it will be handled when it comes back).
Or, if you prefer, just push the locking lever to the right and push down on the barrels. If the shotgun has been stored for a while, it may be stiff.
I prefer the first method, you may prefer the second method.