Just a quick taster from GZG's upcoming Light UNSC Heavy Weapons pack.
I personally like this style of Javelin meets AT-4 Spigot man portable Medium Anti-armour Weapon. It takes the modern into the future and beyond. Whilst the power, lethality and versatility of a soldier's personal weapons will increase within our lifetime. let alone the far future, it's likely the counter-measures and protection afforded to valuable military hardware will increase likewise or not more. There's always going to be the need for something a man can carry that will pack a punch against a variety of targets. The bigger the target, the bigger the punch required.
That tube may house micro-missiles, fired individually or in unison, maybe electronic chaff or microbot dispensers, an EM pulse or a single powerful plasma energy bolt.