That belt is the "crimp groove" . It is of little concern to me at firsts. More important is if your present COL will cycle though the magazine and chamber without jamming into the rifling.
Generally what I would do with a new bulet is first see how long I can load that bullet (COL) in a dummy cartrige before it touches the rifling then back off .005. Then try that length in the magazine and see if it cycles through the magazine. Single shots are so much easier of course.
On a hard kicker that is what that belt is for.. so you can crimp on it and stop the bullets in following rounds from getting inertia pulled while sitting in the magazine. Every thing has a trade off. Seat out long to near the rifling and ususally accuracy gets real fine. But if the bullets move on recoil you have to stop that.
A Lee Factory Crimper gives the option of long seatint but still crimping (you can overdo that).
Mike in Peru