So this is simple. Allow me to explain a few things real quick before someone starts screeching about how [Heavy Caliber] is bad.

[Heavy Caliber] reduces accuracy, and generally that is a bad thing. I mean, it seriously effects this weapon. So why is it here? Area Saturation. This build is for closing down very large areas. So with that qualifier out of the way, let me walk you through this.

The Mods

Cautious Shot- You can drop this if you have [Primed Sure Footed] or otherwise don't care about falling down. If you dumped this, I would suggest either [Ammo Drum] for additional ammunition reserves or [Vigilante Supplies] to help keep up your stock. Granted a Max Rank Merciless mod also increases ammo reserves by 100%, which is super nice.

Serration and Heavy Caliber- Base Damage mods and as I explained, I want the accuracy to go a bit off. Sure I wish it was a more mild penalty, but this isn't a huge problem. Besides, base damage mods buff [Nightwatch Napalm]'s damage. At least, that is my understanding. Basically, this is just more damage output.

Galvanized Chamber and Aptitude- These could be replaced with [Split Chamber] and [Rifle Aptitude] respectively if you don't have these mods. Chamber giving us multishot, which is nice more rockets. You will get up to 3 rockets pretty quickly and then the fun really begins. The Aptitude gives us stat chance, which is good, obviously, with the galvanized version giving us additional damage per status inflicted.

Primed Cryo Rounds and Malignant Force- These are your elemental mods. You can swap them out as you see fit, although I do recommend at least one of them as a dual stat mod to keep the status chance over 100. [Primed Cryo Rounds] are really nice to have because of the extra damage you get to have. This is obviously set up for viral, which is my go to sort of build.

Primed Firestorm- We need to spread the love around. [Firestorm] is a great stand in, in you don't have the primed version. Also I strong recommend wearing either the [Furax] or [Furax Wraith] as your melee and making sure you have the Amalgram [Furax] Bodycount mod on there. It gives you a little extra AOE range and that makes me happy. We are about excess here.

Finally.

Nightwatch Napalm- This is the mod that sets the [Ogris] apart from other launchers in my opinion. Having a secondary damage field that just pumps heat and death into targets over 90% of your original impact site is very VERY satisfying.

Final Comments and Considerations

So the chosen arcane is Merciless. This weapon won't be getting headshots. Like. Ever. You'll build your stacks up super fast and it will be super fun. This weapon does fine in steel path, granted it doesn't kill super fast like some other weapons do, but it does basically make sure trash mobs stay trash mobs, no matter what it is you are doing. This weapon is not a single target nuker, but it can soften things up and it will dump stacks of status procs into larger targets that don't have a status proc limit or immunity. Which is like. All the super awesome bosses, which is a bummer. Also, it is STRONGLY recommended to have the Arcane Healing doodad on your warframe as if you take a tic of radiation damage and are effected by the proc, you might kill yourself and your whole team. Its happened a time or two to me and I really feel like I need to warn you about that. Lastly, progenitor element I used is Radiation, but most others will be fine. I suggest radiation because it causes more chaos and its fun to watch survivors of your mayhem shooting each other, instead of you.

Feel free to leave a comment telling me how poor, mediocre or good you think this build is. I am always looking for ways to improve this gun. I just wanted to share this build because I have seen a lot of really mediocre builds pop up on this and I have no idea why people are sharing builds that would have difficulty even clearing the base star chart.