I just got a new set of dies so i could start reloading my .243
i sized, cleaned, primed, powdered, but when i started pressing the bullets in to them they fall inside the case

the bullets i am using say 6mm. but under the 6mm they say .243 to the best of my knowledge they fit both
everything i have done to verify this comes up with the same thing (comparing numbers and dimentions in the nosler book

so now i need help what is wrong why is the case not holding the bullet
and how do i remedie the problem