Thunderhead & Lightning very very frigthening

Perks:

• Born Ready - Basically required for Big Bertha with a 55 mag size.
• Vampire - This is just for self-reviving with Iron will, you can take something else here if you prefer.
• Thorns - Build is bad at dealing with jellies and swarmers so this is almost a requirement.

* Iron Will * Dash (Basically just to buy time for born ready if you mess up your CC/mine placement)
Grenade: Any but probably team-killer/incendiary (Sticky is not really needed since Big Bertha with fear will turn Praetorians around and shred them very quickly, you can kill \~3 per magazine) Pickaxe: Damage (Pretty much just for Oppressors)

Big Bertha does a ton of armor break and direct damage, its downsides are lack of CC, being surrounded/flanked easily and having a hard time reloading. Fear instead of feedback loop on tier 5 helps remedy this. While firing at enemies that are closing the distance fear will tend to scatter or push back those that would get through letting you get a few more shots to kill them. Super helpful when trying to keep a hallway full of enemies back. Feedback loop isn't super useful since the amount of time you spend at foll RoF with Big Bertha without mag size mod is relatively low. When you run out swap to the BRT, electro minelets are surprisingly good now and offer a lot of utility. They can very effectively keep you safe for 5 seconds while you reload big bertha. Electro mines and fear utility:

• You can fire through the first row of enemies and set mines on the ground behind them for the next row of a wave to hit.
• If enemies are coming down a wall you can fire through enemies and set mines on the wall to trip up the rest.
• You can hit web/acid spitters and menaces with the stun and set mines on the wall/ceiling under them which will trigger before the stun wears off to finish them.
• Menaces pose very little threat for this build.  Big bertha can do a lot of damage and send them fleeing until they borrow, stopping their attacks. And the BRT can be fired at a slow pace to keep them stunned until the electro mines pop and begin electrifying it. Anything you fire at it has a good chance of stopping its attack immediately and doing significant damage.
• When fleeing a wave and waiting for born ready on Auto Canon you can fire mines in front of you and run over them. The will arm as you run over them and trigger on whatever is chasing you creating a lot of distance.
• When getting ready to fire big bertha and hold a position you can set mines behind yourself to help catch flanking grunts. Born ready will reload it before you empty Big Bertha's mag.
• Big Bertha with fear makes very quick/safe work of mactera. They get shredded very quickly and the fear keeps them flying around instead of shooting. Once you get used to swapping targets to keep them fear'd you won't need to drop a shield when a flight of mactera appears out of nowhere.
• Big Bertha fear will naturally turn praetorians around giving you a lot of weakspot hits. You can kill around 2 per mag this way.
• With all the CC you should almost never need to shield to survive, you can save them for teammates and resupplying.

Surprisingly this build works in pretty much any situation. Big swarms, Dreadnoughts and haz 6 are no problem. Haz 7 is doable however the electrified effect is not as effective as CC since the base speeds are higher, still doable you just need to be hyper vigilant. Once you get used to the flow of combat and how the CC works, surprisingly you can handle haz 5 double enemies with this build as well as long as you position well. The only one I would not take it on is swarmageddon+lethal enemies.