MgT2E - Just browsing the various weapons systems it doesnt appear anything other than the largest planet buster has a chance to take out a decent military vehicle without hitting it several times and rolling really well on damage. Am I missing something.
Okay, after looking through my books, I have a few comments, some of which I have already mentioned. I do need to note that I have MgT 1e and Supplement 6: Military Vehicles (2300AD used the revised version of that for it's vehicle designs), so my numbers may not match what you are seeing.
(1) Armor is too high: Based on designs in S6, I think the armor of the military vehicles in 2300AD is about double of what it should be. The problem here is that there is no way to find out how much armor in S6 a given amount of armor in GDW 2300AAD is worth. Indirectly in T2300, 1 point of armor is 1 cm of hardened steel. Unfortunately, in S6, there is not even an indirect reference as to how much real world armor a point of armor represents. Therefore, conversions are mere guesswork, and for this book, wrong guesses were made. Additionally, the plenum chamber, which was poorly armored in T2300 is not even a target in M2300.
(2) MgT underestimates shaped charge penetration: This actually should vary with TL, with early HEAT rounds being Semi-AP or AP, eventually getting to at least Mega-AP or Ultimate-AP. However, possible the result of flawed simplicity, it was just set at Super-AP. While shaped charge warheads are much better at penetrating hardened steel than long rod penetrators (eg, APFSDS), it is much easier to degrade their performance with armor add-ons (such as reactive armor) while long rod penetrators can really on be further degraded by thicker armor or more advanced armor. I think S6 chose to simplify this this by ignoring all the add-ons to defeat shaped charge warheads, Unfortunately, this is done at the expense of realism.
(3) Anti-missile systems: The heavier 2300AD military vehicles mount one or two anti-missile systems, so even if your missile has the right penetration listed a single missile is highly unlikely to hit.
This isn't 1945 and your character isn't a Volksturmmann stalking a T-34/85 in the ruins of Berlin with a Panzerfaust.The odds of a lone infantryman knocking out a MBT with a man-portable missile is technically non-zero, but not by much.