Is there a mag FAQ?  Something similar to Troy's excellent piece on the AR mag board?  I have a gew questions - why three types of construction (steel, polymer, bakelite)?  Purpose, durability, cost of production of each?  History/reason for the brown polymer 5.45 mags?  What fits in what without mods?

TIA

This page doesn't answer all of your questions, and it only approaches the quality/thoroughness of Troy's site, but it may still be worth a look:

linx310.nothingbutguns.com/magazine.htm