Leaving a lube groove exposed won't hurt a thing, except maybe picking up some grit along the way- but honestly, has that ever been a problem for anybody?
My favorite flat nosed bullet is a 190 grain with a very wide meplat of .2", from out of an old Saeco custom mould that dates back over 30 years to when I was involved in cast bullet matches. Unfortunately they never catalog it. It was designed for a perfect fit in a specific .30/30 match barrel neck/throat, and serendipitously has been almost magical in every .30/30 and .303 Savage I've used it in since then, and a lot of other .30 calibers.
