Yeoman, I tried 209's (fpj) and personally did not see any advantage in using them in this style gun, and #11's work perfectly. Never had a misfire or delay fire, and they are cheaper, and easier to use for me. I know 209's will give a crud ring with some powders, #11's don't.
Maybe Sabotloader will chime in, I know he's done quite a bit of shooting with the different ignition systems in MK's.

Your barrel is most likely a green mountain. Only the very early models had barrels from other manufacturers. I believe they went to GM exclusively in 1989. Gm's have 8 lands, I believe some of the others had 6.