[PlasticGuy]

In Washington, a security guard can carry anything that an LE officer would be allowed to carry, so long as they can pass the state qual with it. That leaves it pretty wide open. Companies can (and almost always do) make their own list of approved weapons and loads. Most common around here seems to be Glocks, though you do see a fair number of Sig and Beretta pistols. Some guards for low budget companies carry some oddball stuff though.