You can use grease as some have mentioned, but it will hold moisture and still rust your choke. Unfortunately I know quite a few guys with stuck chokes in there Novas. Many will never be coming out without a gun smith or replacing the barrel.
I switched to Nikal made by Jet Lube. It is a pure nickel extreme service anti-seize lubricant. This is the best stuff I have used. My buddies all use it as well. Great stuff.
When you insert the chokes, pull them up until they are just past snug. If you crank down on a choke you will stretch the threads and may form a permanent bond with the barrel galling the heck out of the threads. Many choke manufactures make chokes for the Nova as it is a popular waterfowling gun. I would start with shooting the modified choke. Until the marketing geniuses of the world started pushing chokes many folks used what they had and killed many birds. If you have extra money in your pocket I am sure the shooting industry would appreciate you buying chokes.
