Are you referring to recoil? The Eldar shuriken gun uses some sort of gravity pulse to launch extremely light projectiles at a very high rate of speed. There is no significant radiation produced. Presumably there is some recoil but the gravity pulse uses probably blunts it to a significant degree.
A more real world analogue would be a rail gun, using electromagnetisim to propel a bullet. This would produce a small effect on the wielder, but the EM fields generated are extremely short ranged and cycle very quickly as the bullet passes by each magnet. The recoil would be significant though, just as if the bullet was fired by a chemical source.
Lasers DO produce EM, but by their very nature it is DIRECTED radiation, so there isn't much "backsplash" on the wielder unless they are shooting into some sort of reflective substance. But even this wouldn't reflect much since the laser would heat up the target and turn it into plasma. A pulsed laser, firing in microsecond pulses, would have even less reflection since it would burn through the reflective medium in staggered bursts. I suppose if the laser was being used in a really humid atmosphere that could absorb and radiate heat there could be some IR radiation transmitted back to the wielder, but in general this isn't an issue because if the laser is heating up the air the weapon then ther are other more serious cooling issues to deal with, see below.
Unless the gun is shooting something like gamma rays that could penetrate through the side of the weapon, or is powered by a nuclear charge, it doesn't seem like the wielder needs to worry about backsplash.
For kinetic weapons using a chemical charge, there will be a significant blast, which can kick up a lot of surface material and produce a shockwave if there is an atmosphere to conduct it. There shouldn't be a significant fireball unless there is excess chemical residue that continues to burn once the bullet leaves the barrel. This is common with battleships/artillery since they stack extra powder charges into the chamber to manipulate the shell velocity for a given range. In a military rifle with specific ammunition, powder reside and "flash" is minimal since the exact correct powder amount can be used and what is used is low flash anyway (since a large Hollywood style fireball is a great return fire indicator :)
If firing a significantly large kinetic weapon beyond what a person can hold easily, recoil compensation can include shooting something out the back of the weapon, aka a "recoilless rifle" or bazooka. In this case, the wielder has to be aware of what is behind him since there is essentially a rear rocket blast that counteracts the recoil of firing a large or very fast projectile. Scale this up and you would need substantial hearing and eye protection, as well as some body armor since a lot of debris can be kicked up by the blast.
Heat from weapons is an issue. This is usually dealt with by ejecting a heat sink (i.e. the brass cartridge), firing in short bursts to allow for some air cooling, and eventually replacing a hot barrel. But you can water cool a machine gun, or use spinning barrels like a gatling gun. There is very little heat transferred to the wielder since he can be easily insulated from hot weapon parts via a stock and grips of low conductive material. A laser can't dump heat like a conventional machine gun, so it will need some sort of cooling system. Radiation fins could generate enough heat to affect the wielder (basically like standing next to 1000 degree heating coils).