Dual ATM12 has 72 burst at 120-270m. That's pretty nice, especially with faster targeting from the LTAG. Now some people might try getting within that 120m. Then the big shotgun gladly greets their internals (though honestly, it doesn't mind doing that at 270m either). The ATMs are high mounted and can fire over many ridges. If the ammo storage is not safe enough in the arm, try moving a launcher there and keeping the ammo in the LT. This is also the way to run this build on the ON1-IIC-B variant, and because of the larger arm hitbox, it's slightly harder to lose both ATMs at once. Invest in survivability on top of the quirks, mobility for being better at brawling, and some ammo skills to keep firing if you would run out. LBX and Missile nodes as you see fit. UAVs are also nice!