The way you control neck tension or bullet grip by sizing without the expander ball is to outside turn your neck thickness. For example, if you are sizing for a 30-06 and:
Your neck thickness is .014"
Your sizing die sizes the neck down to .330"
You want .002" bullet grip
then the math would be
caliber - bullet grip = desired ID of neck .......... .308" - .002" = .306"
die dimension - desired ID of neck = total brass thickness ........... .330" - .306" = .024"
total brass thickness / 2 = thickness each side ............. .024" / 2 = .012"
So if you outside neck turned your brass to .012" then you could size your brass without the expander ball and have .002" bullet grip .............. theoretically
I say theoretically because there are some other variables that will have some effect, namely springback which is a function of the softness or work hardening of your brass neck and how accurately you can outside neck turn to an exact .012".
If you really want to get exact then it helps to have an accurate way to gauge the ID of the neck. I use pin gauges
they measure to the .001" but you can tell additional information by how easily or difficult the pin gauge goes in.
IMO bullet grip is also affected by the condition of the inside of your neck. IOW any scratches, burrs, left over lube etc. will also affect bullet release and seating depth variances. To solve this problem I use scotchbrite and mica
I recently did a test where I size with 3 methods on 5 case each and gauged the resulting bullet grip.
Regular sizing die with expander ball
Bushing style Redding neck sizer
Lee Collet Neck Sizer
Using the pin gauges and to the best of my abilities, I came up with the following conclusions
The Lee Collet had the exact same ID throughout the 5 cases. IOW the same pin gauge went in with the exact same resistance.
The expander ball did almost as well using the same pin gauge but with varying resistance.
The bushing neck sizer varied between three pins with it tight on one side and loose on the other side of the center pin size. These case necks were outside neck turned to the best of my ability.
Lots of ways to skin this cat but doing it this way my velocity extreme spreads have mostly dropped to the single digits and my groups have shrunk at the longer distances.