You can quick draw a pistol and fire in one action...
You can't use pistol with your Longarm skill.
...but you can quick draw a machine pistol and fire as one simple action using Automatic skill
- and still use Automatics Skill for your assault rifle
The CQB option of Longarms skill is Shotguns.
(but in SR5 core you might as well continue to use the sniper rifle in CQB over a [slug loaded] shotgun).
There's another big draw to SMGs - they're one handed...
Which is yet another reason that make Automatics skill even more versatile compared to Longarms skill...
The more I think about it the more I like the house rule that get rid of automatics skill.
Pistol cover all firearms you can hold in one hand and longarm all firearms that require two hands.
Also strange that you don't get any benefit from using a SMG with two hands.
...one would expect that you get a recoil compensation bonus of one point if you use it with two hands
(or less recoil compensation due to strength if you use it with two hands)
btw- In real life SMG is a weapon you normally use with two hands while braced against your shoulder.
There is an advantage of using an SMG vs a Sniper rifle in close combat, something there aren't good rules for - noise.
In SR5 core you need a perception test with a threshold of 1 to notice gunfire
...and a threshold of 2 in addition to a negative dice pool modifier of 4 dice to notice silenced gunfire*
In SR5 core you have the same chance of hearing a high caliber sniper rifle as a low caliber pistol
...or an assault rifle equipped with a suppressor as a pistol equipped with a silencer.
(exception being the Ares Light Fire series that give the target a negative dice pool modifier of one extra dice)
*But depending on your reading there might be a threshold of 1 in addition to a negative dice pool modifier of 4 dice for noticing suppressed gunfire and a threshold of 2 in addition to a negative dice pool modifier of 4 dice for noticing silenced gunfire. However, it should be noted that SR5 core does not seem to make the distinction between the two.
Earlier editions of SR made a distinct difference between a Silencer and a Sound Suppressor.SR3 p. 281 Silencer
A silencer is a barrel-mounted accessory that reduces the sound and flash of a weapon's discharge. Silencers can only be used with single-shot or semi-automatic weapons. They cannot be used with revolvers. A silencer applies a +4 target number to any attempt to notice the weapon's use, or to locate the weapon's firer. Using a silencer modifiers Concealability by -2, and requires one Complex Action to install or remove.SR3 p. 281 sound Suppresser
Similar to silencers, sound suppressers are used with burst-fire and full-auto weapons. A sosund suppresser adds a +2 target number modifier to any attempt to notice the weapon's use or to locate the weapon's firer. Sound suppressers must be replaced every 300 rounds of burst of auto-fire. A sound suppressor modifiers Concealability by -2, and requires two Complex Actions to install or remove.SR5 p. 432 Silencer/suppressor
This barrel-mounted accessory reduces the sound and flash of a weapon’s discharge. It cannot be used with revolvers or shotguns. It applies a –4 dice pool modifier on all Perception Tests to notice the weapon’s use or locate the weapon’s firer. Attaching or removing a silencer takes a Complex Action.
Wireless: The silencer/suppressor features a Rating 2 microphone with Rating 2 Select Sound Filter and simple software that alerts you via AR if your silencer detects the sound of someone nearby reacting to the sound of the silenced weapon.