Problem with seating die

[Poconolg]

I fully prep all my brass by checking full length, Neck diameter outside and they are all the same with a measurement of.252 which is very light neck tension. I brush the inside of the necks before and after neck sizing. I am using Redding comp neck sizing dies with bushing.
What is meant by a donut? The press is fine works good and I keep it lubed. Bullets that were used were all from the same box. I tried 2 different brands of bullets.

 

[David Christian]

Type “donut” into the search bar and you can read to your hearts content. Slide a slightly undersized gage pin into one of your sized cases and see if it gets stuck at the neck/shoulder junction. Small bulge of brass that forms in this area due to brass flow. Donuts are why some people turn necks.

 

[Metal God]

Im thinking some sort of inconsistence with seating force . What that is Im not sure . The Redding comp seater stem is resisted by a spring . It sounds like the force it takes to seat the bullet is causing the spring to flex different amounts on each seating attempt. The donut could do this , work hardening may do this . Gunk built up in the die it self could cause inconsistent focre . What ever the cause , my guess it’s the spring force that is the ultimate issue , why that is could be a few different reason .