I wanted to start a forum for people who were getting frustrated. Seeing quite a bit of hate on the Chiron, especially the explosive artillery variant. One can fight this variant as early as their 3rd deployment or so, if you unlock the diplomacy mission for either Synedrion or New Jericho, so I will try to keep my advice low-tech.
Do not just start firing your guns on turn one.
Unlike Xcom, its possible to be able to perceive an enemy, and not to be perceived (Ignoring the concealment mechanic). A Chiron will not attack you, even if other enemies see you, until it hears something or sees you. If a Chiron hears you, it will fire where it heard the shot being fired. If the Chiron does not perceive a threat it will use ALL its movement to go basically across the map, you’d be surprised how often the artillery charges to the front lines when it doesn’t know there is danger.
Take the Warcry skill
Firing the weapon takes three action points. With Warcry, you have a thirty tile range(including rocket jump) to shut down any artillery, which should be do-able if you follow the previous tip.
Sorry if this is offensively obvious, but getting indoors before YOU fire the first shots can help avoid the rain of green death.
Break its head
A Chiron has a willpower pool of 30, and breaking its head (which is never armored), will reduce the maximum will to 10. You can do this with any sniper, even a poorly outfitted one, fairly easily. Even if you cannot reach the Chiron, you can manage its will and stun lock it through panic.
It has low ammunition
It only has 5 rounds, and with stability stance, it will only fire twice at full gusto, and then one normal round, meaning the unit is useless after three rounds. If the creature is firing at the structure you are in, it will likely be out of ammo before the cover is completely useless.
Bring a Scarab
This vehicle is worth more than I can type in this forum, but it can protect you as you move around, or waste the Chiron’s ammo. You can fire a weapon for 2 action points and then re-enter the vehicle, and you can use abilities, like Warcry, and then enter the vehicle after if needed. etc. etc.
Anyway I hope this helps some people.