Basicaly, if you have ever thought of an explenation for odd things that don't make sense in video-games, post them here... even if they contradict a thing or two in the game, or the official texts.
Now, most of us know that, except for the Beam Rifle, none of the Covenant 'Plasma' weapons in Halo/2 make sense; as is explained on
stardestroyer.net, they travel too slowly, among other things, to be plasma weapons.
Bit of a stretched idea, but perhaps, rather than plasma weapons, what the Covenant in Halo2 are firing are, basicaly, artificial ball lightning.
Ball lightning is usualy reported as 15-40 cm in size, and that's easily within the size of Plasma Rifle/Pistol Shots. This could also help decently explain why these weapons are so much more effective against, not only the Master Chief's shields, but his armor than they are against standard Marine/ODST armor(Marines/ODSTs have
FAR more health than the Master Chief in Legendary...); he uses what effectively is a
powered-combat armor.
As for them being called "Plasma" Rifles/Pistols, I don't think I've ever heard the Covenant themselves call them such, and humans don't understand them well, so it could be explained that they generate plasma as a by-product of the generation or firing of the actual shots, but not enough to have any practical use, which would explain why when you get... over-enthusiastic with them, they overheat and large amounts of hot gas(plasma) come out, and when you fire, you see a little puff of similarly colored gas. Perhaps coolant is being turned into plasma?
The Humans apparently don't know much about how Covenant "Plasma" weapons work, so they may just know that they somehow involve plasma somewhere, and decided to call them "plasma" weapons.
Of course, this is in contradiction with the instruction manual, but Bungie's to blame for calling them plasma weapons in the first place anyways.
