The 1/2 inch diameter turrets on many AQMF models are, in scale, about 4 feet in diameter. This seems big enough for one man, cramped for two men. A single gunner-loader (one man) could work for guns up to 4 inches in diameter, with shells weighing up to 50 pounds. A 5-inch gun has a shell that weighs about 75 pounds (including propellant and brass) This is a bit too much for one man to deal with. (Yes, friends, when I was in peak shape I could dead-lift 200 lb and curl 50 lb with each arm. To expect even a strong man to work a 5-inch gun alone without blowing his own a$$ off is a bit too much. Humans are just human.)
My suggestion: in scale measurements
1/2 to 3/4 inch turrets can have a single man and up to a 4-inch gun.
1 inch to 1 1/2 inch turrets can accommodate up to a 7 inch gun;
3 or 4 inch guns in a larger turret might get a higher rate of fire in a turret this size.
2 inch turrets can accept a gun up to 12 inches.
Part of this is to be a guideline for turrets/emplacements on the battlefield.
A 12 inch gun fires a projectile that weighs over 700 pounds. The propellent is in separate bags. To load a 12 inch shell, the projectile is lined up with the breech and placed with a hydraulic ram. Several bags of propellent are then rammed into the breech and the breech-block closed. The gun is then guided into firing position. 2-3 rounds per minute is a good rate of fire for a 12-inch gun. A WWI era AP projectile from a 12-inch gun can penetrate 16 inches of steel armor at 1000 yards. That, to me, is awesome.