Which 209 kit did you install? Rem or cabela's(jobber)? If Rem do you notice a delayed fire? I have a fair bit of experience with the rem 700 mls, having owned 2(still have one) and shooting/hunting with several others who own them as well. The fellas who used the Rem 209 experienced many problems with it& 777 (mostly pellets but loose as well) with getting reliable ignition. The fix was either the cabelas kit or 209 nipple and 26# spring vs the supplied remington one. Or going back to the #11 and shooting either pyrodex pellet/loose or 777 loose. If the cabelas one then scratch the above!

I have the cabelas 209 and never experienced a problem. I shoot 209W primers exclusively. 95 gr ffg T7 with 240 xtp and green mmp(hornady packaged) sabot produceMOA groups as long as I can. 2 x 50's of pyrodex or 777 pellets would easily hold 2" @ 100. So unless your ml barrel is heavily plastic fouled or loose I can't see these being the problem. As mostI know use such a load with excellent results. If the sabot is really easy to slip down the barrel try the short MMP HPH series and 45 cal xtp vs the 44. If it is really grippy feeling try scrubbing the bore with some plastic removal solvent and bore brush (shooter choice mc 7, etc remove plastic as well as lead/powder fouling).

BTW, I swab between shoots using the 50/50 solution and technique provided by cayugad. Though even when not for follow up shot testing does my group suffer as badly as yours did. So it leans me to a problem with scope or rings/bases. Since you'll try the iron sights this should tell you if these are your culprit!

What are you using to shoot off? Solid rest or free hand? I like a solid bench and sandbags for developing then practice field positions once I have found the load I'll be using. Eliminates shooter error some!

Good Luck.