Complex sentence: There are also some shotguns measured by diameter, rather than gauge, these are the.410 (10 mm),.380 (9 mm), and.22 (5.5 mm); these are correctly called ".410 bore", not ".410 gauge".
Split into simpler sentences: There are also some shotguns measured by diameter, rather than gauge. These are the.410 (10 mm),.380 (9 mm), and.22 (5.5 mm); these are correctly called ".410 bore", not ".410-gauge".