Ask H&K -- or the British Army. H&K burned through at least two gargantuan contracts to fix the British L85 bullpups and the upshot of the whole thing is that -- they still stink. SAS carries M4A1s, mostly, and won't touch the L85 with a bargepole. The rest of HMs Army has no choice but totes the L85 around. Bullpups are a good idea that are yet to have a good implementation.
The French FAMAS is almost as bad, but then again, it was designed only to be dropped or stacked...
d.o.l.
Criminal Number 18F