First break the seal by using a seating die and pushing the bullet a few thousands into the the case. This helps whether using a hammer puller or a collet puller.
If you end up buying a hammer type puller get an RCBS, WAY, WAY down the road when it does break it guaranted -- forever. And forever is a long time.
Also remember the collet puller is caliber specific and doesn't work well with pistol cartridges whereas the hammer puller will pull just about any caliber, pistol or rifle.