Some questions on the topic:
1) Would it be practical? Are there any problems with going bullpup (other than having to re-issue the rifle to everyone).
Define "practical". The bolt lockup could remain the same, but the bolt carrier would have to be completely redesigned as the existing extends into the buffer tube, as would the lower, which for legal purposes is considered the rifle. You could keep the original charging handle, I suppose, but it would be crazy awkward.
So, legally speaking you would be making a new rifle, and in practical terms, there wouldn't be a lot of the original rifle left once you were done. I suppose a ZM weapons upper would be a decent place to start.
2)Is it possible? I would assume so after redesigning but then again I don't design firearms. >_<
It's possible... although it might be easier to melt down the stupid thing and forge an entirely new rifle out of the slag. ACE rifle stocks was trotting out a prototype bullpup:
http://riflestocks.com/images06/ARBP/ARBP-ss.jpg
But there's not a whole lot of AR-15 left underneath it all since it's piston operated and has a new carrier, charging handle, etc. It's about an AR-15 as much as the L85 or bushmaster M17s is.
3) Would the reduced overral length make the M4 obsolete? After all, I read in another thread the 5.56 round fires poorly (i.e. to a poor effect) with it.
Until someone makes a bullpup with a length of pull similar to a completely collapsed M4 carbine so that it works well with body armor, has all the controls up front where the strong hand can manipulate them (excepting the magazine well, which is pretty much unavoidable), I doubt that they will completely supersede existing designs.
The Kel-Tec RFB and Steyr AUG are the best thought out bullpups, from a pure design standpoint, in my opinion. The RFB doesn't just tackle trigger pull and ambidexterity issues, it takes a running leap and pitches their lifeless bodies over the edge of a cliff. Note that it has only 8 inches behind the barrel, while most .223 bullpups need 10!
Alas, it's a touch heavy, there's no way to check the chamber without removing the magazine, the barrel is difficult to replace, and the magazine release is still in the rearward position. It remains to be seen whether the tilting bolt will compromise accuracy and primary extraction the way it's sometimes reckoned to in other designs.
The AUG has an acceptable degree of ambidexterity, and the fastest change barrel of any assault rifle, not just any bullpup. Length of pull and trigger pull are not so good, however, magazine release is still completely rearwards, and I hate crossbolt safeties with a passion (and you should too!).
So, if someone could just figure out how to crossbreed those two, we'd have something pretty nice on our hands. A pity that they don't appear particularly cross-breedable.
