Different Ammo types are required to balance the AC2 & AC5 IMO, not new armour types.
Yes, but different type of ammo requires additional work. If it'd be simple & good solution than we'd have it since beta 1
We don't have ammo types, so we have the light armor - plays identical function.
Yes, but that does nothing to the AC2&5 vs ground vehicles, that imbalance is still there, and the creation of another armour class is just a bad idea as it necessitates the uber/nerf weapons and Rock Paper Scissors imbalance for example:
You can hit a VTOL with a UAC20 (Rock), the VTOL (Paper) shrugs it off and wanders away (I've done this) whereas a few mgun rounds and AC5 slugs (Scissors) and the VTOL falls out of the sky, all due to the magic of "Light" armour. You can fire the same AC2 slugs all day long at a 'mechs torso to no noticeable effect (ergo Rock Paper Scissors).
Battletech uses a hitpoint system, it's one of the fundamentals of the gamesystem, and influences such things as why 'mechs are armed the way they are, why they just don't have 1 BIG gun capable of destroying any machines in 1 hit (instead of the mix of weapons most carry), and why every weapon in the game can inflict the same amount of damage on any asset in the game. It's a fundamental baseline in the BTU. It's how CBT avoids being Rock Paper Scissors.
@Rally, I would agree but your out of scale by some orders of magnitude (what your describing is the CBT machine gun and not any of the smaller autocannons); the 1st Battletech Book describes the AC5 on the 45ton Shadowhawk in depth, they're 90mm shells, fired automatically from a cassette of 10 that are loaded from the Magazine by an autofeeder; so when the pilot pulls the trigger a burst of 90mm shells pour out of the gun (these 10 rounds are viewed as 1 shot in CBT), now assuming that these cassettes are reloaded as fast as the LB5-X is in MWLL, you've got AA fire snaking into the air, with very little gap in between if you chain-fire 4 of them. That I believe is much better than just making the AC2&5 just a copy of the mgun, would take a little more skill too, so it's all good by me.
There are proximity grenades (Claymores) in Crysis already, there's also grenades launchers (in Crysis as a weapon attachment & Warhead as a gun). Switching ammo type code is also in the Korean assault rifle (FY-72 or something) already, where standard and incendiary rounds are available.
Now imagine those AC5 shells were Crysis grenades with a proximity trigger and a slightly changed particle effect, any loss of damage from RoF would be replaced with splash from the air-bursts. We'd have our skies filling with flak, and a AA weapon that didn't just feel like yet another machine gun. Use it against 'mechs and you'd knock them around while slowly melting their armour all over, which is much more fun and points worthy than legging.
Switch the ammo types to anti-vehicular and you've got the cassette of HEAP 90mms back, no real splash but better penetration (more damage to a single component).
Ultimately I'm not an expert, but I understand the amount of work the Devs have already done to get things to where we are, and I appreciate that. I think the AC2&5 (and therefore the UAC2 &5) need some loving in this game and hate the fact that they are worthless against anything other than ASF, VTOLs and BA.