for the record, ME's method of changing ammo types was a huge waste of time, the inventory management was horrible.
And i hated ME2 for simplifying it too much
Then again, i also hated me2's method of ruining the perfectly executed heat buildup method of play, but thats another story.
AP-ammo consumption is certainly a novel idea, but I am kinda wondering how you plan on working that. Surely, weapons like snipers and such will use more AP, but then ive taken a liking to using bullet-time as a sniping tool (similar to the infiltrator's ability in me2) as it really came in handy.. I am kinda worried that the incredibly limited AP pool in fo3 will kinda start hurting if too many things are dependent on it.
Although I have been meaning to give ap bonuses on levelup, but ive been too lazy to work out the ap calculations