20ga buckshot sweet spot is 35 to 45 yards max(20ga slugs will be the most effective in this case). Definitely use a 3"shell for the extra payload is your shotgun has a 3"chamber here: budsgunshop.com/catalog/product_info.php/cPath/656_2081_10000861/products_id/712000579/FED%20PREMIUM%2020GA%203/quot;%202%20BUCK%2018%20PELLETS%205/50/ If you do not have a 3" chamber, use : budsgunshop.com/catalog/product_info.php/cPath/656_2081_10000861/products_id/67294/Federal%20Premium%2020%20Ga.2%203/4/quot;%20Magnum%2020%20Pellets%20#3%20Lead%20Bucks/ I would personally use the 00 buck load here since there are no standard 00 buckshot loads offered by the Big manufacturers : http://wolfhillammo.com/20-gauge-specialty.aspx

The reason that the big manufactures don't sell 00 buck in the 20 is that it just does not hold enough pellets.

yes 20 Ga buck shot is very effective in short range deer hunting under 50 yards. Any good known brand of buckshot will be fine. Just try out the brands and sizes you have available and find what works best in your gun. People will tell you to use the most open choke (IC or cyl) but with lots of testing I have found that most of the time (not always) a modified choke works best. For 20 I would recommend #1 buck as 00 and 0 buck just don't have enough pellets in the 20 ga.Uuse a 3 inch shell (if your gun can handle 3 in shells) to get more pellets in each shell