I guess it depends on the steel parts. I’m sure there are other magnets.

In any case, if the firing pin or hammer or anything in the trigger mechanism is steel, it’s going to be difficult to move to actually fire.

Say the bullet has a steel tip or core though, and we are able to fire it. The force pulling that bullet is going to prevent the bullet from going much of anywhere. Let’s pretend the barrel and firing chamber are frictionless and indestructible.the bullet will leave the gun, but immediately curve into the magnetic field, inevitably into the MRI itself, but likely not very far.

It would be pretty fun to watch though.