Winter's said that he's tried to get the description for techs and stuff as true to reality as possible. I've just been thinking about some things that probably deserve a mention in the UFOPedia, but won't require any coding changes or modelling changes at all.
Antimatter engines:
There should be a mention as to how the radiation from a proton-antiproton reaction is contained in the antimatter engines. Antimatter reactions produce deadly amounts of gamma radiation, and we don't want to turn every landing site into a fallout zone. Alien materials could probably stop gamma rays, but there needs to be a way to stop radiation coming out the back end, or from turning the propellant radioactive.
An alternative design is to use the antimatter reaction as a power source to heat up a propellant, shooting it out the back end like any other rocket.
Not to mention is how easy it would be to detect these engines in space. Current technology can detect the Space Shuttle's main engines from Pluto, and its RCS thrusters from the asteroid belt. (Yes, I stole those numbers from atomic rocket
http://www.projectrho.com/rocket/rocket3w.html.) Probably the best way to get around this is to 'jump' in (or whatever the FTL device is called) to the upper atmosphere, otherwise a network of satellites in orbit would be able to detect incoming UFOs before they even reach Earth.
Plasma Weapons:
The current method of using a heat-resistant plastic to contain plasma is a roundabout try of getting around the 'plasma weapons don't work' deal, but it still doesn't quite work. Some months back, somebody posted the idea to some forums and they pointed out that this plastic would make near-impervious armour.
Last night, though, I thought of a different idea for the weapon. Instead of bothering with shooting an ionized gas and containing it, maybe the plasma gun actually shoots a superheated gel near its high boiling point (1000 to 3000 Kelvin). The gel is stored cold, and is only heated when fired. A fired shot would have the same effects as the current system, including a blaster shot's explosion through splashing and superheating of the area.
A grenade would spread this gel all over, combining napalm-like effects with concussive force.
In this version, plasma could instead refer to the process through which the gel is heated. The gun could heat hydrogen to a plasma state, and inject this into the gel in order to rapidly heat it. The ionic charge this gives the plasma/gel would allow magnetic accelerators to fire it. Once the gel is in flight, there's little to keep the plasma contained, and this leaks out and gives the projectile its glowing trail.
This gel could have undesirable properties at room temperature, restricting its use as armour or insulation. Perhaps it could be a powdery, caustic substance that reacts readily with air.
Machine gun:
I'm worried about the plastic belt the rounds are chained in. If it disintegrates upon exposure to air, then the magazine must be kept vacuum sealed. This does not sound like a reliable, rugged weapon for the battlefield. Bits of plastic from a partially-decomposed belt link could also get into the mechanics and jam the gun until they evaporate completely. Worse, if the case is damaged, air can leak in and disintegrate the chain before it is even loaded into a gun, rendering an entire clip useless.
I hope you don't mind these suggestions, Winter, I'm just trying to help.