Duck shooting
Mike George
There are some light steel loads, which can be fired through guns of normal (rather than steel shot) proof, but they should not be fired through chokes tighter than half.

Possible damage to tightly choked would be consistent with that caused by the repeated use of any over-pressure cartridge.

As I see it you have two alternatives: either get that tight choke bored out to half, or use one of the softer alternatives to lead, such as tungsten matrix or bismuth.

When choosing steel shot cartridges to fire through guns which do not have steel shot proof, always go by what it says on the cartridge packet and, with older guns, seek the opinion of an experienced gunsmith.