the assumption that the gun has full and modified choking, does not agree with the proof marks....you state that both barrels are marked "choke 18.3 over 18.2 (mm)". that would indicate that both tubes have one tenth of a mm constriction - which is .004 of an inch....about what would be called skeet 1. the barrel length (25.5") would also point to open chokes...as a general rule.
unless actual measurements of the choke constrictions show otherwise, the gun may not be well suited for squirreling.
best regards,
tom
