cookieman -
bird hunting is singularly the best time ever !!!!! i'll assume you will hunt with dogs.
if the dogs are going to be pointers i would use a 20 gauge with 7/8 oz of #8's and a modified choke is fine, an IC or cylinder would work just as good, let the bird get a little bit away before you pull the trigger.
remember, take head or tail shots, otherwise you get too much lead seasoning in your breast meat. don't do the "Pull-Bang" or you will not eat what you shoot.
if your dogs are flushers, the ones that run around chase and flush a bird without waiting for you, i would use 1 ounce of #7 1/2s with a full choke, the birds can pretty far away if the dogs start ranging. a full choke and 1 ounce will work good out to 40 yards.
#4's will pretty much ventilate the bird and really arent needed, this can drive feather fragments, bowel contents, etc, into the meat. you will find little black circles in the meat from this.
don't over choke or use big shot. start with pointers, you have much more control over the hunt than when using flushers. and remember, head shots !!!!
most of your first hits will probably not be clean kills, you may need to manually dispatch them before putting them in you bag so worrying about shoot size and choke is inconsequential.
a vet friend of mine who i hunt with stated that the best way to bag a bird is to shoot when the shot you use and the distance you shoot at doesnt cause pellets to penetrate the feather covering. the kill mechanism is a fast hydrostatic shock to the birds circulatory system from being hit by the shot cloud. he is right in my opinion, but you have to hold off and shoot when the time is right.
have fun and let us know how you do !!!
sg
[EDIT]
p.s. i do use a 410 on all birds but contrary to what MSP said, i do occasionally miss !!!
