To be fair, Rigger 5.0 does specify in the optional drone weapon mount rules (which you must be using for this to even be remotely possible) that a Micro sized weapon mount can fit "Single-shot bullet or dart". So it's not like you're going to be mounting a Light Pistol or anything even remotely pistol sized on it.
Unfortunately, there are no rules for this kind of weapon (yet), so you'd have to house rule it.