Scale: Tamiya's 1/350 scale USS New Jersey and USS Missouri kits' turrets are 11% overscale, closer to 1/315 scale.  These 3D-printed turrets match the Tamiya turrets' scale but are shaped and detailed more accurately.

Set includes 3 turrets with barrels.

Recommended for the Tamiya 1/350 scale USS Missouri BB-63.

This set of three-gun turrets (more properly called "gunhouses") represents the enormous main battery of the Iowa and Montana class battleships.  These model turrets are scaled to fit Tamiya 1/350 scale kits.  The turret apron diameter of these turrets is 39.75 mm, a good match for your Tamiya kit's barbettes.
 
True 1/350 scale turrets are available separately.

Note: when compared to official US Navy blueprints dated 1940, the Tamiya kits' parts are actually overscale, closer to 1/315 scale, about 1/16th inch too wide and about 1/8 inch too long, and the barrels are set slightly wider than they should be.  This design matches the Tamiya turret's size but these turrets are shaped and detailed more accurately than Tamiya's.  Because these 3D-printed turrets have a more accurate shape than the Tamiya turrets, some adjustment to other aftermarket products like photoetch may be required for best fit. 

Features:
dimensions scaled from scans of original builder's blueprints and confirmed by measurements taken from actual gunhouses on the real ships (Tamiya's turrets are slightly too big)
barrels integrated with a trunnion permitting the modeler to set the barrels to any realistic elevation from +45 degrees to -2 degrees, just like the real turrets
open armored rangefinder viewport shutters
rangefinders with telescopic sights visible through the open shutters of the armored covers
armored rangefinder hexhead bolt and domed screw details
detailed rooftop periscopes
asymmetrical underside ventilation trunks (as-built 1943-1945 configuration)
turret roof plate screws, properly numbered, sized and located
 
© Model Monkey LLC.  This 3D-printed product may not be copied or recast.
 
Regarding the Mark 7 gun, from Wikipedia: "These guns were 50 calibers long—or 50 times their 16-inch (406 mm) bore diameter which makes the barrels 66.6 feet (20 m) long, from breechface to muzzle. Each gun weighed about 239,000 pounds (108,000 kg) without the breech, or 267,900 pounds (121,517 kg) with the breech. They fired projectiles weighing from 1,900 to 2,700 pounds (850 to 1,200 kg) at a maximum speed of 2,690 feet per second (820 m/s) with a range of up to 24 miles (39 km). At maximum range the projectile spent almost 1½ minutes in flight. Each turret required a crew of 79 men to operate. The turrets themselves cost US$1.4 million each, to which the cost of the guns had to be added."

This turret is suitable for:
BB-61 USS Iowa
BB-62 USS New Jersey
BB-63 USS Missouri
BB-64 USS Wisconsin
BB-65 USS Kentucky
BB-66 USS Illinois