With the fast burning pistol powders, because there is so little of it in a case, you need the magnum primer to ensure they light because there often isn't enough powder to cover the flash hole. It is why we used to use a thin paper wad over the powder then fill with corn meal. It keeps the powder in place. Some guys used Dacron to do the same thing but results were more variable with it.
That is the whole beauty of Trail Boss. It is large, flakey and fills the case pretty well even at 1000 fps. In that case, the standard primer works better, and the heavy bullets ensure even ignition, a small crimp helps too. Some guys have tried to use pistol primers, which I do use in 22 H for standard and sub loads but I did not find they worked as well with Trail Boss as the regualr rifle primers do in larger cases.
