Clean the molds really well, especially around the pins. Mine get buildup after a while and won't close completely like you're experiencing.
If that doesn't work, keep in mind the molds are pretty inexpensive, around $25. The corner of my 9mm mold got rounded off a bit where the sprue plate attaches, so I simply put the plate in a vise and bent that corner a bit.
Last edited by chris in va; November 7, 2011 at 10:43 AM.