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I am using a 870 with a rem choke barrel I ordered from Remington with the factory XF choke. Using W-W 1oz #6 it consistently put 105-110 pellets in a 10" circle at 40 yards. At 25 yards it consistently put 150+ pellets in 10". I would give them a try. I killed a nice bird at 29 yards with the golden pheasant load.reflexl
I would go 7 1/2s just because I know they have the energy to kill cleanly out to 35 yards, I don't have a ballistics program so I have no idea what the 8s would be good to. Now your pattern will determine your max range but to me I wouldn't go smaller then 7 1/2. Maybe some one with a ballistics program will read this and say what distance 8s are good to.