Is it an extended choke and ported? I had that happen to a turkey choke (one day of rain, and BOOM rust). I took the barrel off and put it in a vice clamp, took a metal punch that could fit through one of the ports and turned and out it came.
If it's not extended all of the above may work. A good soak in PB Blaster, 3 days or so and crank on it. Good luck! I would not advise on hitting with a rubber malet or anything. A buddy did that, his gun shot 2ft to the left for the rest of it's life haha
Thanks for all the tips I will do the hairdryer freezer after I get a new choke tube wrench . No one suggested to but I was thinking of shooting about 10 # 8 leads through it with the hopes of freeing it up . Sorry guys but after one uses a gun for a paddle or in the case of the 88 a step to get out of a hole , the best it gets is a shower to wash the sand out of the cracks . Yes I know exactly why I'm having this problem .
my go to home blend for really bad chit is 50/50 of ATF and Acetone. make sure you have something metal like an old coffee can to put this in as the acetone will eat through most plastic. I got one of those old style metal oilers that I use to keep the blend it to squirt on stuff. had much better results with this blend than any store bought stuff and I think I have tried just about everything out there on the market and watched a bunch of youtube videos on test folks have run using different products.