Mother F`ers are a light weight shoulder exercise, i do them with 10s and they are screaming by 10.

Set up a bench a little under 90 degrees
Kneel on hit with belly down on bench
Start with arms down on other side of cushion part on bench
Go straight up (shoulder raise)
Keep arms parallel to ground while you bring each arm to side (somewhat like flys)
Go back to the shoulder raise position
Back down to the other side of cushion part on bench

This should be done very slowly, about 6-8 second long rep

hope i explained well...