Very true.
Yep.
I have shot at pumpkins with my .50 BMG. The pumpkins were just sitting on top of some RR ties. They didn’t budge at all. And the pumpkins didn’t explode… the bullets simply left a clean, half-inch diameter holes through the pumpkins. 
So I was kinda disappointed that the .50 didn’t obliterate the pumpkins. But then I discovered something that would… a 12 gage shotgun. A 12 gage slug hitting a pumpkin is much more impressive than a .50 BMG round. Pumpkin guts flew everywhere. 
I didn’t know this exact figure, but that probably accounts for the famous effectiveness of the .357 Magnum. DoubleTap’s 125-grain load gets about 1750 fps out of a 6" barrel, and their 158-grain gets about 1540.
DoubleTap is some high-performance ammunition, though.
But what about if you have a machine gun and can spray multiple bullets into the target? That would provide a constant force.
Actually, that is Newton’s third law. For every action there is an equal and opposite reaction.
Oops yes, I was copying from the other forum.
So the answer is no, which given everyone’s input here makes perfect sense now.
In the game, BTW, the guns automatically calculate distance to target, atmospheric pressure, weather conditions, etc and then shaves off an appropriately sized round from a stock of metal and fires it. 
The hammer rounds were explained as being designed to mushroom out, thereby imparting maximum kinetic energy into the target. But even so, as you all point out knocking down the target is a no go unless the tround continues to accelerate after being fired.
Thanks a bunch guys!
To both the shooter and the target. The symmetry still holds.
If that’s how they explained it, then knocking down doesn’t makes sense. I’ve seen somewhere good comparison. It was along the lines of total energy of .45 bullet equal to 1 pound brick dropped from three inches. I don’t remember equal values and am too lazy to calculate it now, but it was something around that order of magnitude. Hardly capable of knocking anybody down, even with mushrooming, 100% “energy transfer” or other exotic explanations.
Actually, mushrooming will tend to cause a higher efficiency of energy transfer. If you transfer anything less than 100% of the bullet’s energy to the target, the bullet is going to come out the other side (or bounce off, but that’s unlikely for human targets). If the bullet mushrooms inside of the target, it decreases the chance of it coming out the other side. Thus, mushrooming will increase the efficiency of energy transfer.
It still won’t knock the target over, because most of the energy that gets transfered ends up as heat, not kinetic energy.
People here are being overly generalist and taking the average too many times. If a really big, strong guy properly stands as he fires a very large caliber round that does mushroom out to tranfer its momentum (and that does actually make a difference) then it really could knock back an average-sized person or even someone his own weight. Any martial artist or football player will tell you that the third law doesn’t make such things impossible. In fact, if you ever did try to design a weapon that’d do it, then a large “hammer” traveling at a relatively low velocity that deforms at impact would be the way to do it. Points to whoever thought of your game.
The hell you say. I demand that you provide video.
Not to hijack this thread, but that brings up an interesting point: back in 1993, Black Talon hollowpoint bullets were called “cop killer” bullets and “armor piercing” bullets, very nearly leading to the banning of hollowpoint bullets. Ironically, because they do mushroom, they were not prone to overpenetration and certainly were not capable of piercing armor.
Just an interesting historical tidbit that is somewhat relevant to the topic, if not entirely on point.