For Shotgun Choke Tubes, only install them finger tight. They will snug up a bit while shooting. If you have one that is stuck, Start by putting your Choke Tube Wrench in a vise, Remove the barrel from your Shotgun, Set the barrel/choke tube over the wrench, and gripping the barrel, try to unscrew the choke tube. If this doesn't loosen it, you might need a Gunsmith to help!
For parts that have rusted together, mix 50% Acetone (can be found in the paint section of your local hardware store) and 50% Automatic Transmission Fluid. Don't apply to anything that has plastic, as it will dissolve it, but apply to metal parts liberally, let set overnight. If still stuck, re-apply and let set overnight. Repeat until the parts will release. Great for loosening Breech Plugs on Black Powder Guns.
A good recipe for a Great Black Powder Bore Cleaner= Moose Milk= 1 part Hydrogen Peroxide, 1 part rubbing alchohol, and 1 part Murphy's Oil Soap. Cleans up Black Powder firearms in a snap!!