I am heavy weapons guy... and this is my weapon. She weighs 150 kilograms and fires 200 credit custom-tooled explosive cartridges at 532.2 rounds per minute. It costs 8 fucking forma to fire this weapon... at max optimization.
Very powerful weapon. You will actually feel like you're mowing down goons with a giant explosive automatic rifle.
First off, let me address the use of [Heavy Caliber].
200 accuracy confers hardly, if any, actual bonus over 100 accuracy. Now ask yourself this, would you put [Heavy Caliber] on a 100 accuracy weapon for that damage bonus? If the answer is yes, then why wouldn't you put it on this either? To keep the useless 200 accuracy? Personally, I find the weapon too visually noisy and jumpy to make it a real accuracy weapon anyways.
Recoil. I recommend [Stabilizer] over [Vile Precision] because there is a 21k DPS change between the two. You can have [Vile Precision] if you want though, as it's a massive QoL improvement over [Stabilizer].
If you stick with [Stabilizer] like I have, just know your reticle is gonna end up over where you were originally shooting. With that in mind, aim for body shots and get it to kick up to headshots. Once you're at full auto, the reticle will hardly change anymore and you're free to go ratatatatatata.
Versatility. Is something this build is lacking since it's filled to the brim with forma. As such, you will find no room to change elements. Since it's viral, this isn't really a problem except in Deimos where a good chunk of enemies are outright immune to the viral proc and take reduced damage from viral. Therefore, as ironic as it is since this came out with Deimos and has a natural fire element, don't use it there. You will also have a hard time fitting a riven into this, but since the disposition is likely gonna be low for a while, you don't need to worry about it too much. If you DO have a very very good riven (like CC CD MS with harmless neg) throw off heavy cal. It is the weakest link.
Note: I am not blind to the fact I am not using Hunter Munitions in this build which will help more with armored targets in Steel Path. I just prefer more on-the-spot damage in my builds vs the content you'll usually face (level 1-50). If you want you can swap out [Heavy Caliber] for it at any time. Either way, you can still kill level 165 bombards quickly in normal play. In Steel Path however, I agree, use [Hunter Munitions].
Tip for using the alternate fire.
Think of the alternate fire as stone skipping rather than a bouncy house. Shoot it at the ground in front of your enemies and watch it skip like a stone across water, devastating everything in a massive line. If you shoot it directly at enemies, especially in a small room, the thing is likely going to fly everywhere and somehow manage to miss everything, yet knock you around like a fucking gerbil in a speed bag unless you have [Primed Sure Footed] on. This takes some getting used to but when used correctly, it is extremely satisfying to just clear a hallway full of enemies running toward you.