There are neck only dies or you can simply adjust your full length die to neck size only. Unscrew your full length die a few turns and run your case into the die, you will get a shoulder on the neck and then just adjust it down using the same case until you get it right. it will take some trial and error until you get it just right. The primer should still fall out since there is only a few thousandths inch between the two sizing methods.

Here is a link to the same question asked just a couple of weeks ago.
http://forum.hunting.net/asppg/tm.as...ode=&s=#276694