Hand-held automatic weapons are inherently inaccurate, since the muzzel climbs with each shot. This is less true with the smaller and less powerful 5.56 round than with the 7.62 fired by the AK-47 (Kalashnikov) and its variants and the various weapons firing the slightly different NATO cartridge, but this is the primary reason that the current M-16 variant used by the US military and its successor, the M-4, are limited to three-round bursts.   With any automatic weapon, unless it is held in a clamp of some kind, the muzzle moves slightly. This, as well as the fact that the bullets are several feet apart as they travel downrange, pretty much eliminates any effect one round would have upon another. The M-16 and its variants are quite accurate, which would not be true if it had any tumble or wobble, accidental or engineered in.