I looked in my Lyman Reloading Hanbook, and it does explain that primers need to be seated correctly to be properly "sensitized" for optimum ignition. They should be seated to a depth .003"-.005" below flush.I wish I could have just copied the whole thing word for word, but there`s this big bold print in the front that says....(copyright stuff)You can measure the depth of those primers using your dial calipers, if you cant figure it out I could try to post a picture later, or google/youtube it. A safety tip for you, as was given to me, when priming with that hand prime tool don`t hold your hand over the end of the cartridge...or point it in the direction of you`re face.Friend said he never had one go off, but just in case.