Right. One time I seated a moly-coated bullet in a newly chamfered case, then had to pull it. To my surprise, the sides of the bullet had all the moly scraped clean off. Fresh chamfers have sharp edges and if you don't want to give your lead bullets a shave, you would have to burnish them down to dull first. Flaring will expose the bullet to smoother inside neck brass that doesn't shave it.
I'm with Jim on the M die type flare for loading a rifle. The reason is the step it puts in the case mouth lets the bullet sit straight upright, as shown below. When the bullet is set squarely upright in that step, the seating ram starts in straight, too, resulting in measurable less cartridge runout. You can also tell is it more straight looking at cartridges with a neck long enough that there is a slight bulge where the bullet base meets the resized diameter of the neck. With a straight seated bullet, the slight bulge goes evenly all around the case if the neck wall is also even in thickness, where it is often much less even or sometimes all on one side of the neck if you start with a funnel-shaped flare. In a pistol shooting jacketed bullets, it,s hard to see any difference on paper, but with a rifle that reduction in runout shrinks groups.
The shallow microgrooves are fine with cast bullets as long as they go all the way to the root, which is why a fat bullet was recommended. However, I've seen that go too far, too. You will probably have to shoot groups with some that are .310" and .312" before you can be sure you zeroed in on the best choice. If you slug the bore, for my Marlin (deep Ballard rifling) 0.002" over groove diameter shoots best, but YMMV, so be prepared to experiment.