If you plan on using the Shotgun/Rocket Launcher combination, it is mandatory to have the Safety Guard attachement. The Heavy Elite Frame comes with all 8 circuits unlocked, so if you have one, use it instead of the Heavy Standard Frame, as you can save precious tungsten that way. That way, you can concentrate on upgrading the clip and rate of fire for both weapons. Both of them need just one or two circuits to maximize the damage. A good choice for the latter would be the Rocket Launcher. However, if you build the Shotgun out of parts you find throughout the levels, you can add a lower tool. The upper tool of Shotgun consists of a Military Engine with a Conic Dispersal upper tool tip. You can also specialize it for close-range combat with a force gun that will keep your enemies at optimal range. When paired with a long-range weapon - like a javelin - you can create a weapon that is useful in nearly any situation. It is well-suited for use as a primary weapon, especially when upgraded to overcome its main shortcoming: a slow rate of fire. The shotgun is effective at close to medium range and can cause tremendous damage to human and necromorph foes alike.

Once you find the Repair Bay at the end of the Crew Access corridor, go through the door on the left. The blueprint for this weapon can be found during Chapter 4.

Dead space 3 all blueprint weapons