I have new brass for the .221 rem fireball and was going to uniform the flash hole. I have not loaded a small caliber like this before and would like to know if you open the flash hole up to the diameter of the uniformer even in this small rifle cartridge? It seam a little too large a hole. I have a lyman uniformer and it produces a 0.090" flash hole. This cartridge is used in a rifle not the handgun. Is it ok to open up the flash hole on a small rifle cartridge to this diameter? or should I only chamfer the internal surface of the flash hole (deburr inside hole surface).

Personally I think this is a significant question. A couple times I asked if anyone had any data showing the affect of different size flash holes and never got any good answers. roger

There has been a couple of articles written about research done on flash hole size. As best I can remember, within reason, it doesn't make any difference.
Why not ream out a half dozen to .090 and leave a half dozen (dont chamfer the inside or anything) as it and compare them with regards to velocity and accuracy.
And, of course, let us know.