I don't have personal experience with this but have heard rumors, when the 209 ML's first came out, that there were accuracy issues with unsing the 209 primers. Primarily that you would get a "flier" here and there. This scared me away from them so I'm still shooting my Knight Wolverine with the #11 cap. I'm not complaining, this thing is a tack driver but I'm considering upgrading. My question is, have the 209 primers designed specifically for ML's "solved" the issue of "fliers"? If not, I'll stick with what I've got!