Optimal bullet seating to neck shoulder junction

[jrock]

How important is it to keep the bearing surface in front of the neck shoulder junction (NSJ)?

I've read it's to prevent a doughnut from effecting neck tension. If sizing with a mandrel or expander, does that push the doughnut to the outside avoiding the issue? I could see a bushing die pushing the doughnut in but then they don't size right to the NSJ.

I'm mapping out a 7 SAUM for the 180 VLD. With the bearing surface right at the NSJ, it has an expected COAL of 2.97". I would think the bullet needs to be 20 to 30 thou up from the NSJ to avoid a doughnut. 30 thou of seating one way or the other appears to have a insignificantly change in case capacity.

 

[jimbires]

neck expanding with a mandrel does not push the doughnut to the outside . it might push it some , but not nearly enough . I'm forming brass for a wildcat . I'm getting doughnuts during the forming process . I'm inside neck reaming , and also outside neck turning , to completely get rid of the doughnut .
you are correct , bushing dies do not size the neck to the neck shoulder junction .

I'm not sure what the correct answer is on the doughnut . if you keep the bullet above it , it shouldn't matter as far as seating goes . I'm thinking it could be a flex (bend) point when the neck expands to release the bullet , so I'm getting it removed .

 

[jimbires]

one other thought ,I forgot to mention above .

if you would get a bullet seated into the doughnut , will you have enough neck clearance in the chamber ?

 

[dok7mm]

Position of bullet in the neck also varies with proper seating depth, so a given position to start with may effect where your bullet ends up.

I handle possible donuts by getting into the shoulder when turning new brass. I also use full dies without expander balls and follow up with a mandrel. Lucky so far!

Tight dies and loose chambers really over work brass and push shoulder into neck, causing quick donuts.

I always figured 35* and 40* shoulders would have fewer donuts, until I had the problem with 280a.i. donuts. Traced it down to the die being tight & factory chamber.