I can confirm from seven years of recent experience that one ounce of English number 6 size shot is all you need to bring down driven pheasant here in England. I usually use the Hull Cartridge company's Imperial Game loads in a 2.5" cartridge.

After Christmas I go up to the number 5 size pellets and to a 1 & 1/16th ounce load, also in the 2.5" case.

Remember that these birds are being driven towards you so usually the head is hit. Any heavier loads are unpleasant in my 6lbs 12 ozs. Webley boxlock.

HB