what, if any are the negative aspects of not using an expander ball during re sizing?

Under sized neck. (Was that a trick question?)

Depending on the die set you might end up with a tight neck. I have a number of 3 die set (pistol and rifle) that uses a decapping pin then a mouth expander. No expander might reduce the amount you stretch the neck.

You can do it. The neck brass needs to be strong though. The bullet being a little larger than the sized neck can cause the mouth to collapse as you seat the bullet.
I have done this in the past with very good results.
Just so you know, it does not stop neck stretch.

I don't use the expander ball on any of my bottle necked cartridges. I use the Lyman 'M' die to expand the case neck and put a small flare at the case mouth.

jim

quote:

it does not stop neck stretch

Nope "reduce" can be a long distance from stop. The majority of the neck lengthening comes from the brass needing to move someplace as it is resized. BT bullets normally feed just fine in a tight neck. Flat base might cause you an issue.

Thanks everybody, I think I will try the Lyman die.

My die set for 30-06 imo over sizes the neck

I lapped out this area so the sizer ball does very little

On Dangerous game caliber bolt actions and double rifles I reduce the expander ball one to three thousands on a lath or drill press to get a very snug neck and use a powder that compacts lightly with a case full, and then use a light crimp..This method is easy on brass and cases last forever, and your bullets won't move forward from recoil..If you take the expander ball out and can still seat a bullet your chamber is probably overly large or at least sloppy at best. Using an expander on brass cases shortens case life with split necks.