Here are some good targets in pdf:
http://www.uspalma.com/Targets/targets.htm
What MOA is the dot size? If 4MOA I'd think you'd want to try a 4" target at 100 yards. Maybe a bigger one as long as the center of it matches dot size. I've never used a dot sight but I'm curious about the process myself. Post results, good and bad.
peace.
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