Karl talking of greying out may have to with shooting next to the wall indoors and a muzzle brake on the end which directs expanding gas to the sides, which is then thrown back at the shooter in this confined space. I have only shot G3 on fun setting on open air ranges and they were controllable and keep the bullets on a three men target built from these:
But overall the G3 twists and turns each cycle in all directions before it straightens itself again for the next shot. Definitely not easy.
C8 is essentially M4. The gas port location was largely driven by ONE factor. M7 bayonet.
The M4 barrel length is totally random anyway. Driven by the totally important requirements of mounting the bayonet, the M203 grenade launcher and that it does not blast eardrums like the 11,5" short carbines that the XM177 and CAR-15 had been. One quick fix taped to the other to make it work somehow.
Instead of looking into ballistics like muzzle velocity, how to make it function reliably through timing of the events during firing cycle etc. as was done for the C8. Had they put the longer AR-10/A5 length receiver extension and buffer in it they would have checked all the boxes. But you know that already.
Edited by Panzermann, 04 August 2017 - 1529 PM.