Not really sure about the MG-34, but I know the MG-42 had the booster added to the muzzle to increase dispersion because it was too accurate/had too small of a cone of fire. In general, LMGs (unless they have a shortened barrel), MMGs, and HMGs are really accurate in single shot and 2 round bursts. 3 round bursts on just about any gun aren't great because the 3rd round tends to fly off anywhere due to barrel harmonics alone, hence all the weapons with 2 round burst mode instead of 3 these days. Even an AKM has an accurate 2 round burst, I can tell you that from experience. Also, the higher the RPM the more accurate a 2 round burst will be (look up the AN-94). Unless the RPM is slow enough or the time it takes for the gas block to fill is long enough that the shooter/recoil has time for the barrel to re-align to the target before the 2nd round exits (which is the case with an AKM). That's all perfect conditions though, shooter's capability excluded. Iron sights, you'd be lucky to hit even a standing man at 400 meters with a bolt action rifle. The finnish sniper Sama is one of the greatest in history and that was about his maximum effective range for irons.
Marksmen (not snipers) and MMGs are said to be effective at 600-800m due to 2 reasons for the most part- 1.) having a spotter to help adjust shots and 2.) watching the tracers. Not to mention already knowing the ranges in his fire arc and where the target is in said arc.
Anyway, my personal opinion is that the single shot on the MGs is perfect, the 2 round burst should be more accurate (the 2nd round flies too high), after that I could care less. 1-2 rounds is what it's going to take to get the kill, if you're dumping off longer bursts there should be more targets and your range to the enemy should be close enough to get the hits. If anything, start your burst at the knee. Technically the MG-34 should be a tad more accurate than the other MG in short bursts due to fire rate difference and just overall mechanical difference.
