M4
Could be me, but I had become very used to the 16 with a 203 strapped to it, so my first issue was a 4 with the 203 which made it very front heavy and unbalanced. And firing the 203 from it was not as accurate as from the 16, this could have just been the amount of practice that I had with the 203 on the 16, but I really felt that it was a disadvantage. The weapon wasn't as accurate on the KD range, but like I said before, in the UC range it was worthwhile. The barrel seemed to have a tendency to climb and the flash is enormous, not the best if you are trying to shoot and scoot. I had no problem with the reliability and the collapsable stock was nice when you are trying to negotiate through heavy bush or doorways, but it didn't give me a good sight picture. It seemed to be too short all the time no matter what position I hd it in. The new ones I am told have more adjustability, plus if you remove the 203 and add the handle, it makes a difference in controllability in a heavy fire fight at close qurters. Might not be good reasons, but they are reasons.
Semper Fi....