I am trying to figure out what fixed chokes are in my American Arms 12 gauge o/u silver?

Question

there are three diamonds on the bottom barrel and 1 on the top.

Answer 1

Usualy the top is full choke while the bottom is open or modified. over the years someone could have changed them , the best thing is to have them measured ,any gunsmithe could do that easily. he may have a plug for checking.

Answer 2

Take it to your local gunsmith and have it checked