I don't own a M3, but I do own an M1. For the life of me I can't see why someone would spend the extra 300 dollars to get an M3 when they offer so little in return. The ability to pump the action is great if you are planning on using specialty rounds such as door busters that won't cycle the action. Otherwise it's useless.
bkm...
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Anyone worth shooting, is worth shooting twice...