3B" you definitely need to flare your case mouths a little more to accept a bullet with a square base. If the base is square, and the case mouth is square and smaller,,, They won't go together. Period!
You can just get a Lee Flaring Die which is totally adjustable to create any amount of flare you want and they are like $10.
Or you can use Boat Tailed Bullets which will go in the hole.
Randy