Hc certainly not doubting you. I think it must be for a case capacity reason or possably to insure that all brass comes out the same regardless of brand or type. if you ream it all then it will all end up close to the same. if that is the reason then personaly I would try to get some quanity of the same type of brass and just neck ream if you stick to the same type of parent brass then you should be able to come up with a good consistent load. this is a case were you need to seek out the experts. personaly I dont like messing with the base of a round as it is unknown waters for me. can you post the instructions or other links to this? it is very interesting stuff to say the least. perhaps leaving a lip inside causes cracking or some thing????