I'm gonna buy this and stick it on the back of my BA3A I got used.

New "lobster tail" from Adept. Three thin steel plates rated to VPAM PM-3, covering 9mm FMJ at over 1,400ft/s. $198, designed to work with the novasteel but can probably be jury-rigged to other helmets if you're creative.
It's clearly meant for riot-but-maybe-guns type work. The company is still shady and certless but credit has to be given, they've got some interesting ideas.