Well, cultists are a real workhorse unit, more than chaos marines.
If you compare the cost of 10 naked marines (140 pts) you can see that you could have been able to bring in 30 cultists with 2 flamers. This means that you get more bodies, more attacks on the charge, more resistance to morale checks due to shooting....
Marines should have a purpose in the army, cultists can just be trown in droves to try and kill stuff.
I usually run them like this:
-10 with 1 flamer & ccw / pistol
-20 with ccw / pistol
-30 with 3 flamers & ccw / pistol
if i run 30 of them i usually join Huron or a slaanesh lord on steed to infiltrate/outflank them and make them fearless.
The shooty configuration works better in multiple small units: this allow you to better direct your fire without overkilling and give the cultists more survivability.
So, if you want to shoot:
10 cultists, heavy stubber, 5 autoguns (60)
10 cultists, heavy stubber, 5 autoguns (60)
10 cultists, heavy stubber, 5 autoguns (60)
10 cultists, heavy stubber, 5 autoguns (60)
Lots of bodies, 4 units, lots of basic dakka.
This configuration can be extra funny if you take the Helcult formation, where you have fearless cultists units and meatshielding a raging helbrute. It's a formation, so no objective secured, but fearless and 3+ cover is gold.
20 Cultists, 15 autoguns
20 Cultists, 15 autoguns
(210)
1 Helbrute, power scourge, multimelta
(115)
And you have 24" covered against hordes and even vehicles.
As a side note, i suggest you to ally with Renegades and Heretics and field the truly performing Renegades platoons. They have better special weapons, better options, cost less and can have autoguns for free...
Allied detachment---
renegade command squad
autocannon
(55)
renegade Platoon (270 pts total)
20 renegades
chaos sigil (auto pass the first morale or pinning test each turn!)
3 grenade launchers
autoguns
Militia training (BS & WS 3)
-90 pts...
20 renegades
chaos sigil (auto pass the first morale or pinning test each turn!)
3 grenade launchers
autoguns
Militia training (BS & WS 3)
-90 pts...
20 renegades
chaos sigil (auto pass the first morale or pinning test each turn!)
3 grenade launchers
autoguns
Militia training (BS & WS 3)
-90 pts...