Lapua 7PRCW turned brass develops dounuts?

[1banger]

I got some new Lapua 6.5 PRC brass. Neck up to 7mm and turned the necks down to .013 average using an IDOD neck turning lathe.
I am used a PRCW turned neck reamer to cut the chamber. Everything works as expected except after the first firing
I am seeing and external doughnut on the shoulder to neck junction. This prevents the shoulder from seating all the way into the chamber.
I had to re-turn this section to remove them. I have not had a chance to fire this brass again yet.

I am to expect the doughnuts will return after subsequent firings on the brass?

 

[memilanuk]

Are you sure that's actually a donut, in the traditional sense? Typically those manifest *inside* the case, at the neck/shoulder junction.

Or is it an unsized section of the neck, due to a radius at the bottom of your neck bushing and/or a floating neck bushing riding up a bit in the die?

If it was due to sizing, you might have just made that area at the base of the neck *really* damn thin...

 

[RegionRat]

Sometimes this is caused by being shy with the turn and by allowing too much headspace.

Be sure your outside turn is going all the way into the shoulder, and don't allow a generous headspace.

If you keep having the trouble, you will want to share photos with Bryan over at FCP and see what he thinks.

 

[1banger]

During the Initial turning session, I made sure to get into the shoulder about 50 thousandths or so to try and avoid the
brass in the shoulder, flowing into the neck during ignition. When I size the bushing is locked down, no float, and seems to be engaging
the entire length of the neck.

I will be firing some of the re-turned brass today to see if it comes back. Thanks for the comments!

 

[straightshooter1]

During the Initial turning session, I made sure to get into the shoulder about 50 thousandths or so to try and avoid the
brass in the shoulder, flowing into the neck during ignition. When I size the bushing is locked down, no float, and seems to be engaging
the entire length of the neck.

I will be firing some of the re-turned brass today to see if it comes back. Thanks for the comments!

When I read your OP, my first thought was . . . "sizing with a bushing die???". Even though your bushing is "locked down", you're still going to get a small portion of the neck that isn't going to be sized. And after first turning with the IDOD, I don't think it's a good idea to cut away that unsized area of the neck, as that just seems like that might make that area too thin resulting in the neck eventually separating???

. . . just my thoughts.