Which probably ain't to much compared to a chemichally powered projectile of similar kinetic energy. I doubt it could shoot a weightclass 8 or 9 suit backwards. How would the HRR suits handle that then?
I'm more curious as to what kind of force the slug exhibits on chitin-armored aliens. You could then calculate how many spacebugs you can efficiently turn into space-goo. Welcome to the blender. Softdrink of the day - "Biomass 9000" containing all the energy you need to create 9001 chibinids.
Know your physics
Railsguns have a thousand times higher maximum knetic energy, because they are not limited by the Speed of Sound in the explodign Gas. They are only limited by how much energy you can pump into it. Wich is why we research rail/gaus guns as the Future weaponsystems. (en.wikipedia.org/wiki/Railgun).
Also do not forget that so far they only fired or even aimed the gun while standing, never flying. Because it has an insane recoil to reach kilometer long ranges.
the way to launch a projectile (chemical or railgun) is almost not taken into account for recoil. (it's even a bit worse for chemical, as some of the propulsive energy is lost as heat)
basically, your kinetic energy will be mass * speed^2, this kinetic energy being imparted on both the launcher system and the projectile. (of course, as the projectile has much less weight than the launcher, the speed the projectile gains is much more important in comparison to the recoil suffered)
nevertheless, we don't use railguns for the moment because we principally need to devellop a good enough power source to power it.
That doesn't look like a railgun
It looks more like a proyected energy weapon, like a huge laser cannon. Otherwise he wouldn't been able to completely vaporize that Durchii bitch. If that is the case, it should have almost no recoil, as the mass of light is close to zero.
Actually it's not the issue of powering a railgun that makes them hard to use, we have easy access to nuclear reactors. The issue is since unlike Gauss Guns the slug in a railgun is touching the rails after about the third shot the riles are pretty much destroyed.
So until we make an alloy of some kind that can survive launching projectiles at that speed while still being conductive it's impractical to use one.
No offence, but unless they changed it in the latest codex, kroot can use guns. Not many kroot gunners are seen on the tables because the tau are usually better with long range weapons. But tau are bad in close combat, something that the kroot are expert in, so they are used as blocker or meatshield. This explain why almost all the kroot auxiliaries are close combat oriented.