A modern soldier will typically carry upwards of 200 rounds of ammunition; inthe Forces, our standard load was five magazines and we would have stuffed a few more in our pockets, so give me 30 rounds times 7 = 210.
Could I have killed a whole slew of dudes? You bet, but not as many as you would think.
To use, say the “Braveheart” version of the Battle of Stirling Bridge (which happened in 1297, long before any of the participants would have seen a gun) as an example (that particular battle did not actually go that way, aside from the fact that it was a lopsided Scottish victory, but it’s close enough to a typical battle of the time to work for this discussion) suppose I’m plopped down next to William Wallace and somehow we understand each other’s English enough for him to grasp that I’m on his side. All of a sudden shit gets real. How many English can I kill?
Well, firt of all, the fuckers are already within archery range. I would have been way, way better off being plunked down about a mile from their encmapment the day before, when I could have snuck up on them and started plinking guys from 300-500 metres away from a concealed position. As I am now in archery range I might be dead in ten seconds. I don’t havea shield. Thanks, Disposable.
But let’s pretend William and his buddies immediately understand the value of my boom stick and cover me with their shields while I start shooting. I sill can’t kill the whole English army; I only have 210 rounds. Furthermore, there’s not a hope in hell I will kill a man for every shot. I’m an excellent shot, but it doesn’t take THAT long for those guys to cross 200 yards or so of ground. In that period of time - let’s say it takes them 30 seconds to get to me - I can at most take 8-10 decently aimed shots. My best bet is to kill their generals, which should be pretty easy to do - they’re the really easy to spot guys in bright uniforms who I’m about to shoot off their horses - but still, in 30 seconds I’m not going to convince the entire army to run away and then all of a sudden I’m in a sword fight for which I am painfully lacking in training. Or swords, for that matter. To survive I’ll have to get up once they’re close and retreat, using auto bursts to cover my retreat, and then I’ll be unable to fire on the infantry because they’re mixed up with my new Scottish friends. All that is assuming I’m not hit by an arrow.
So really the best I could do in line is to kill perhaps 20, 30 men. From a concealed and distant position I could kill many more but no more than I have rounds, which given a standard loadout isn’t THAT many guys. The English had no fewer than ten thousand men.
An infantryman by himself really isn’t much. Armies are armies because they work together, using combined arms to exploit every strength and cover for every weakness. A proper army is a sort of giant game of rock-paper-scissors, where each combat arms capability has situations where it dominates and situations where it will be dominated, and the deployment of your arms must be designed to account for this.