My 358 JDJ is a rechambered factory 35 Rem TC, SSK did the work in 1995.
I took one each (444 Remington / 444 Starline) and resized them first in a 444 Marlin sizing die to square them up. For this exercise I screwed the 358 JDJ sizing die in the press so it touches the shell holder at the very top of the up stroke. That said, I have my die set so my cases receive a crush fit when chambered on the closed action.

Where are you setting up your die?

Both cases were trimmed to a length of 2.220. I used a Speer 180 grain flat point seated to the cannular grove.
Using ball micrometer, dial indicator, calipers etc. here are my numbers.

Starline 444 brass ? 358 JDJ
Neck thickness = 13.3 thousands
Neck diameter = .3801 inches
With the bullet COL = 2.779 inches
Neck diameter with bullet = .3848 inches

Remington 444 brass ? 358 JDJ
Neck thickness = 12.6 thousands
Neck diameter = .3768 inches
With the bullet COL = 2.777 inches
Neck diameter with the bullet = .3864 inches

With the Barrel OFF the action and held in my bench vise - BOTH rounds chamber freely with no resistance.

Let me know you need anything further.
D..