The lore states that Elerium engines have 99% efficiency, and with no moving parts either, the waste heat would be very low. I also took the liberty of making Plastasteel a heat superconductor, which makes it ideal material for a radiator (and possibly allows ramming through air at Mach 6+). Let's us also not forget that Elerium is more of a energy-storage-molecule than a conventional fuel; batteries usually have high efficiency. However, I do not believe in reactionless drive. I'm not a physicist, but basic newtonian equations point out that such a drive would have an infinite acceleration, which is naturally BS. So it's quite likely (and that's my opinion) only behaving like a reactionless drive, in reality it interacts with the gravitic field of the universe in some fashion. Such 'trick' technology seems to be very much in line with the cunning ways of the Star Gods.
However I noticed how large and empty UFO hulls are in relation to the size of engine. My theory is that you need so much bulk of 'Plastasteel' hull to somehow dissipate all the heat. It might be that personal arms are simply too small to allow more power than Heavy Plasma without too much heat building up.
Clips/magazines issue: while weapons have magazines, I'd wager that you buy and manufacture clips (why pay extra for the casing?). But in battle, you use magazines (except for things like Hunting Rifle). However, an item cannot have two names. Hence, I think that clip is a more fitting name in general, if imperfect. It's the same as with manufacturing 'arrows' while what you see in battle are arrow quivers.
