The Constructor appears similar to the Manager. The barrel is 2 normal barrels under a Manager Drone Creator
The Constructor has no attacks and instead creates Sentries that have 15 health and shoot bullets at 1 bullet / 0.5 of a second (or 1:0.50). On death a sentry will hand out 372 XP on tier 1, 582 on tier 2, and 1,302 on tier 3
It takes 5 seconds to make a sentry and to upgrade one. Upgrading a sentry requires 100 XP (if your xp is less than 23K, you cant upgrade or build sentries, and instead fire bullets that do 15 ingame DMG at most. This is also achievable via right click)
As the Constructor
Make sure to set up defenses
Against the Constructor
How do you kill machine guns? Do that.