To be stealthy you need to have a suppressed weapon right? With a shotgun it is obviously impossible to add a suppressor. Well... Is it?
Of course we can suppress the shotgun; You just have to follow my steps.

Step 1: Choose any class (Recon, Assault, Breach and Sniper).

Step 2: Use the SA-12 Shotgun as your primary.

Step 3: Use the M92 with any ammo type (FMJ, JHP)

Step 4: Apply Medium armor and the Serellan Patch.

Step 5: Equipment 1 = Grenades and Equipment 2 = Breaching Charge.

Step 6: Save your loadout and check if your shotgun has a suppressor.

Step 7: Of course try it.

This loadout can work Online and Solo. AI will not react to shotgun from far range when suppressed.

If this procedure does not affect your Shotgun then I do not take action or responsibility.

Thank you for reading and I hope this helps your tactical ways of Takedown: Red Sabre.