Tim,
FWIW, I have a an 870 Wingmaster of '69 vintage, I think, serial # S2113XX-V, a 3" 12ga. that gets used for ducks w/steel shot. It does not have the fortune to be wearing anything more than a plain full choked bbl. and it has been shot and carried enough that the checquering is worn fairly smooth in some places. The bbl is unaltered and unrecalled and it shows no signs of distress whatsoever, no choke ring-bulges, no pressure rings in front of the chamber, no nothing. I don't know exactly how many steel rounds have been through that bbl. but at a minimum several flats .. as in over five. I would not worry about the forcing cones in your gun at all. Also, I found to the contrary of what was being published that if you want full choke patterns from steel at 40 yards on the plate then you should use full choke constrictions .. that is using steel shot sizes of #3 & #4, all that I use, except for some #7 steel target loads that I use as swatter loads, when they are required. Having said that about the 40 yard patterns, try & keep your shots inside 35 yds. w/steel, if you can. I sometimes set the outermost blocks & 'flankers' with a laser range finder at roughly 35yds. Its an inexact science, ya know;-)
