Here's what my cousin (BuckoDuck) and I do:
[ul][*] First off, sit close enough togther so you can whisper to each other. It doesn't bother the birds if done silently enough. We've communicated this way with hens in range and they never knew we were near.[*] Like Barefoot said, decide beforehand who is the primary shooter.[*] When you get the opportunity to "double up" sync your shots by counting DOWN, not up. Like this: three-two-one-BOOM. If you say count to three and shoot, in the heat of the moment someone may start thinking, "do we shoot on three or go 1-2-3-boom?" Practice it with unloaded guns in camp. Listen to the click of the firing pin and see how well you do.
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It DOES work.