How do you tell choke of barrel that's not marked?

To determine the choke of an unmarked shotgun barrel, you can use a choke gauge or caliper to measure the diameter of the barrel at the muzzle. Compare this measurement to the diameter of the bore further back in the barrel; if the muzzle is smaller, it indicates a constriction, typically associated with tighter chokes. Alternatively, you can pattern test the shotgun by firing it at a target from a set distance and observing the spread of the shot, which can give you a visual indication of the choke's constriction.