you will be better off spot drilling the exact center of the radius in the back of the slot , then drilling it out with a 27/64ths drill or smaller, that will rough more of the material out and have the radius in the back of the slot in the correct place. then your 7/16ths end mill wont squeal so bad, and have as bad of a finish. Also rough the rest of the slot out with a smaller end mill because it will flex toward the side of the slot that your climb cutting on. (and smaller end mills are much cheaper)
to everyone else, hi, i'm jeff i'm new, this is my first post but im a long time machinist making high end aviation parts.