Line of battle TAG with an HMC, your goal is to be firing that thing as much as possible. It can be tempting to use it to buff your ARO game, but this is a pure active turn killer and should be hidden when not fighting. Also watch your range bands as they're not quite the same as some more common weapons. Remember you're safe-ish in cover vs combi rifles but anything else starts eating that advantage quickly. Make sure you're targeting the right things. This is your no-nonsense killing piece, use it against MSV troops and anything else that will ignore the advantages of your more subtle/situational foes. One exception is anything that has a missile launcher, it's simply not worth risking your TAG unless you have no other options & are caught out. You're better off w something that can get under it's good range band versus one which lives in it. Missiles and Snipers also outrange you, remember beyond 48" your shots fail, and that can happen on Infinity boards, especially w a big silhouette.
MAKE sure it's well guarded and has places to retreat to, or better yet end every turn out of LoS. Smart opponents might wait until you've spent all but 2-3 orders before revealing that TO hard counter. Good options are a second or third active turn piece that can directly counter MSV, or apply even worse modifiers in exchange, KHDs, and a line of flamethrowers and mines to fall back on. Fear the 'smoke and CC' as most armies can do it & will be considering as a way to get through your armor and gunfire.
As with all PanO TAGs, dont be afraid to take on things that have defensive mods on occasion, especially in your +3 range band. Even -6 in cover you're hitting 50% of the time and you've got a 5 shot burst to hand you a 20% chance of a crit every action. Also, you can take 2 or even 3 gunfights on at a time, with your monster burst, they will all be contested and you'll have a decent chance of winning. Dont overkill grunts one by one, especially if you're up against rifles out of range band.
Use HFT defensively or against things that cant hurt you only. Remember CC 18 looks good until you're up against a martial artist or tied down for a round not firing the HMC. Dont be afraid to intuitive attack something you think you'll take an unopposed hit from otherwise though. [Ideally unnecessary if well supported.]
In general though: it will win the gunfight, that's what you spent 1/3 of your points and 1/2 your SWC to bring.