Assuming that the laws of physics are pretty much the same in the Cosmere. I did some physics to see what the terminal velocity of a spherical object with a radius of 1 centimeter would be through air in standard conditions. I assumed a force of 1500 Newtons which would be strong enough to accelerate a 100 kg man upward at half the acceleration due to gravity. Using (Wikipedia drag force equation).
The terminal velocity that I got was around 3000 meters/second. This is over 3 times the muzzle velocity of most sniper riffles which seem to have a muzzle velocity of around 900 meters/second. So Wax if he stood still enough and had a straight path could get a bullet to travel 3 times faster than a sniper shot. That's pretty crazy.
I don't feel like calculating how much time or distance it would take to reach that velocity as that gets a little more complicated due to drag force being a function of velocity. But still it is possible for a coin-shot to get a bullet or other metal object moving at over 3 times the velocity of a bullet fired from a sniper riffle.
Given that type of velocity there is no way that a hazekiller's wooden shield could stop something at 3000 m/s. So it would seem that it is very difficult to push on an object consistently enough to achieve this type of velocity. Otherwise nothing could stop coin-shots except other allomancers.
Also there would not be very much recoil even if you got your projectile to terminal speeds. The recoil would only be from conservation of momentum. Momentum is equal to mass times velocity or p = mv. Since the mass of a bullet or coin is very small compared to the mass of a human the person would not be pushed back very much. Also you are presumably accelerating the coin from rest so it would be about as much recoil as you would feel if you threw a football.
