hi Juglans, there was a thread here some where, i think it was either Gryphon or Von Gruff posted about calculating mag width, I think they got the details from Olson's book, but thanks again for the info, I ended up finding an FN commercial unit locally so it all worked out in the end, thanks to all who put their 2 bobs worth in.

found the thread it was actually on the African hunting forum-

https://www.africahunting.com/threads/proper-magazine-layout.35015/