I use a Demolitionist Auto Rifle (Shadow Price) + a Demolitionist Fusion Rifle (Riptide) with Armamentarium + Echo of Starvation + Arc Siphon helmet mod. When you pick up an orb (likely generated by your own Arc AR or any gun that has demolitionist + siphon mod) you get Devour. You then use either your Demolitionist Primary or Special weapon to make kills on adds before Devour runs out. Devour refreshes on every gun kill and gives you both health and grenade energy. It took me roughly 18 enemies with my AR and Devour to get 2 Grenades full for Unbreakable. And only roughly 10-11 enemies with my Fusion and Devour to get 2 Grenades full. I am not saying this build is perfect for Endgame or GMs. But it allows you to recharge very quickly your grenades for maximum uptime of the Unbreakable aspect. Discipline is btw. at just 50 with Scatter Grenades equipped (due to it's 1:45 mins base CD).