using neck resizing for lee single stage press. 308. When I go to seat the bullet after resizing it is too loose and sometimes the bullet even stays up in the die.... doesn't this "crimp" the neck at all? Must I use a crimping die to finish the job. Help!

NO, you are not sizing the neck enough to hold the bullet. Crimping is not necessary for 99% of all reloads. Be sure that your die is sufficiently lowered into the press and that the case is raised all the way into the die. A bullet should not be able to hand start into this case.

What kind of die are you useing?