BAR had a low rate of fire, and that tended to spread out the recoil. With that, and the bipod, the bursts were sometimes too accurate, all rounds hitting nearly the same place, not giving enough dispersion to tag an enemy moving away from his firing position.
The M-14 that I was issued and lived with for a year was never as accurate as the BAR. Partly that was due to the lighter M-14 weight, partly due to the higher rate of fire, partly due to the bipod being further from the end of the barrel. Worst jam I ever had was on my M-14 when the firing pin came out the back of the bolt then stabbed its way through the trigger assembly.
The M-16A1 was very accurate in semiautomatic, so much so that it was our preferred engagement mode. By the time the bolt moved, the round was out the barrel. Automatic fire was (back then too high, 750+ rpm) and the recoil added up. Short bursts required concentration. We could sometimes get 10 bursts from a 30 round mag in ideal conditions, but that would quickly turn into one burst if attention flagged. The last 28 rounds would be deadly if a bird was flying low, but unlikely to hit an enemy.
the AK-47 (we trained with Romanian ones) was reliable and easy to field strip, but seemed like someone kicked the whole washing machine down the stairs. Unlikely to hit anything you aimed at beyond 150 yards, but you might hit a lot of things you didn’t aim at.
Never fired an M-4. The shorter barrel gives lower velocity. The 5.56mm military rounds are most effective if they hit meat at higher than 2500 feet per second, and even then only yaw and fragment if they hit with the point not quite on. To meet that velocity number you have to position your target to within about 50 meters (a bit more with the 55 grain rounds), and should try to hit with at least 2 to have a good chance of having at least one round yaw and fragment. Good tactic at close range: Keep firing at known t threats until the threat is gone. Good tactic at long range: shoot one round at known and suspected target positions (subject to ROE concerns with civilians) and keep shooting to discourage enemy from firing back.
Lethality is much less than 100%. Humans tend to survive gunshots unless hit in brain, spine or heart. Brain, spine, and heart are less than 10% of human cross section, though can be more if your opponent is looking over a wall at you with only his head exposed.
Our troops would be far better served if the current flash suppressor was redesigned as a muzzle break.
I machined such a muzzle break for my semi-auto M4 for hunting Jackrabbits in Nevada. My first attempt actually over-compensated and shoved the muzzle down with each shot. That is a very unnatural movement and very difficult to control. After several iterations of machining, I got it absolutely neutral with respect to muzzle jump. The rearward motion is negligible. Now I can just hold the cross hairs on a running rabbit and touch the trigger until a bullet strikes home. The 223 Rem/5.56mm cartridge shoots fast enough and flat enough that a hold over or lead is not necessary out to over 150 yards.
Year, I like full auto fire against those grass stealing bunnies also. My Model 1928 Thompson Sub Machine Gun is a real kick to shoot at running rabbits. On my last hunt I averaged on Jackrabbit per 30-shot magazine. That is a considerable improvement over some of my first efforts.
The only thing more fun than shooting at running targets with a machine gun is to use tracers. It doesn't get any better than that.