The breech moves left and right. It can have one or more turrets attached to it. To have it start facing some other angle in the game, you can use the angle key. To limit the turret's freedom of motion, you can use the min and max keys. These keys specify the minimum and maximum angle the breech can turn.
Speed is controled by a key aptly named speed.
The default value for speed is 100. There are 2 spawnflags that can be set for the breech, the first is acurate. If acurate is set, the turret will figure out where you are aiming and aim at the same thing. If acurate is not set, the turret will simply set it's angle to your angle. The second flag is multiple.