How do the Swivel Matic Bases work?

[longbow]

I know there are two kinds.  One that rotates 360deg. and lock into place like every 10deg or so and one that rotates 180deg. that don't lock.  I am looking at a pair of the gimbal mounted swivel matics that don't lock into place.  I am assuming that the pressure of the cannon ball at depth and the forward motion of the boat keeps the rigger in place if it doesn't lock and the other 360deg uses a pin or something like that to lock it into place.  So if someone could help me out I would appreciate it. That is before I spend my money.  thanks