[VOA]

Just to let posters/lurkers know this isn't a "hit-and-run" question, as I'm posting, then going
to do some work...

But my naive, only-shot-an-AR-15 once question is this:
Is there a reason(s) for not using a bull-pup configuration to give a more
compact weapon, especially since US forces have been making noise about the
difficulties of returning fire out of their HUMVEEs suring hot situations.

Just curious why the bull-pup isn't at least part of the US military small arms inventory.

[tortoise]

But my naive, only-shot-an-AR-15 once question is this: Is there a reason(s) for not using a bull-pup configuration to give a more compact weapon, especially since US forces have been making noise about the difficulties of returning fire out of their HUMVEEs suring hot situations.

Bullpup configurations are have a number of properties that make them less than optimal in many ways. I haven't met a bullpup personally that I would prefer over a CAR15 type configuration. It would be possible to engineer a fine bullpup-ish design, but it would require some significant changes (or eliminations) to the baseline engineering assumptions that are not very feasible within the framework of NATO standards.