So yeah, every body wants one and there seems to be a few who have tried to make flush bottom metal but I've only found one reference to cutting a magazine down and that was on the 6.5Grendal forum, which I seem to no longer be a member of.
So I decided to make a go of it and started with one of the factory 10 round .223 magazines:
First I disassembled the magazine which is particularly easy on these magazines: