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Measured the three expander balls on my various 6.5x55 dies and they are all 6.65mm or close to it or about 0.05mm under projectile dia.

Second try.
How did you go tommygun?

How did you go with this Tommy.gun

Greetings tommygun,
A possible solution, short of a whole new die set, is to buy a Lee collet neck die. You could use your current FL sizing die for the bodies and size the necks as a separate...

Went out to the shed to check,
Both the Lyman FL and RCBS Neck dies resize Norma or Lapua case necks just enough to hold the projectile but nowhere enough for Winchester cases. These dies were...

Greetings,
The problem is likely that the dies are old and designed for the thicker continental brass. More recently the US and some continental brass is thinner and does not size the necks enough....