I have just finished transforming some .220 Russian to 6PPC and came across a few problems.

I expanded the necks, then turned so the would chamber with a bullet in the case.

Fireformed then resized and trimmed the necks.
First problem; the case length was shorter than I would have liked, but not by much after fireforming. I have ended up with cases that are 37.75mm instead of 37.80mm. No big deal.

With the case mouths square I decied to run them through the neck turner again, on the same setting as before, especially since they were a very tight fit.

This time the turner took off very little material, but left a patch on every neck untouched. The same spot on each case. It also took away more brass down near the shoulder.

I suspect that I have come across the dreaded donut I read about in the instructions for the neck turner (K&M).

I will have to use these cases as they are, because I'm leaving for Australia to hunt in a week. I'm not overly concerned at this point, I suspect that the low spot in the necks is due to the die, and would probably straighten out once I fire and turn again, right?

Are these common problems?

It is normal for the 220 Russian to shorten when fireformed in a PPC chamber. As the case walls lose some of their taper and the shoulder angle changes, the case gets shorter. If your chamber has enough freebore the doughnut is not a problem.

the first thing is find the chamber neck size, then figure out what the neck walls need to be (I like around 2-3 thousands of clearence when a loaded round in in the chamber. Set up your K&M turner to cut the amount you want and cut them one time, get it right the first time.

http://www.benchrest.com/forums/ Here is a link to center fire benchrest. The shoot a lot of 6ppc. Do a search or ask there also.

1- both, dull and shiny areas after neck turning indicates that wall thickness is varying,
This is quite normal - to a certain extent. With too much wall thickness and bigger cases than the PPC, you might encounter the banana effect. Variance in wall thickness is detrimental to accuracy- you may want to check cases for this.

2- the donut appears after a while of shooting in the shoulder/neck junction area. It starts behind the bottom of the seated bullet.
It is caused by the flow of brass when firing (when case expands).
To avoid the donut (which may cause the Venturi effect and cause chambering problems), run the mandrel as deep as possible into case. This is an extra process with inline dies.