Neck turning may or may not be necessary. If you're unsure of your rifle's chamber dimensions, turn on a few pieces to test fire so you can check the neck OD on the fired cases to determine if you have proper neck clearance.
When I started my 22 CM, there were no commercial dies available and I sized 6.5 brass down with bushing(s) - with no need to turn necks.
I necked down 6.5x47 brass for my 20x47L. I skimmed the first 50 pieces at the parent case caliber but after watching the NSJ move down into the shoulder after fire-forming, I longer turn necks on these and have no clearance issues.
It's a 1 piece sample, but I recently necked a piece of Alpha 6BRA brass down to 22 cal for measurements. The necked down case grew in length from 1.554" (10 case average) to 1.56" with a neck thickness increase of less than .00015.
DISCLAIMER - I did know my chamber dimensions for both of these examples based on reamer specs.