Autocannon and bugs: High effort gets rewarded.
You might not think about taking the auto cannon with you against Terminids. Generally not being effective against a charger or bigger bugs. Requiring a stationary reload that keeps you vulnerable and the blast radious being quite small for groups of bugs. And at first glance you'd be right. But the auto cannon has 2 things going for it.
It's get fed with stripper clips of 5 rounds which do not go through the bolt.
It has two types of ammo. FLAK and APHET.
Now you might have already put one and two together and realised the point of my post. Never fire your last bullet and be quick at switching out ammo type. For the rest allow me to go a bit into detail. But first thanks the devs for being the kind of gun autists with this attention to detail that makes helldivers 2 so much fun.
The auto cannon is automatic (duh). This means that the action of the gun is triggered by firing a bullet. Ejecting the empty casing, putting in a new bullet, locking the bolt. (I assume the AC doesn't function on a open bolt principle.) As a result as long as there is a bullet in the chamber you do not need to cock the gun. This is true for all automatic weapons in helldivers. If you reload before your weapon is completely empty there is no cycling animation. For most guns though the cocking isn't a time consuming part of reloading. Not for the auto cannon though. Being a high calibre weapon with a toggle lock it takes your helldiver some time to cycle the action. Especially compared to inserting a stripper clip animation. Which is pretty unique because you feed the AC not through the conventional way between the bolt and the chamber but through the "bottom" of the magazine which sits next to the action of the gun and then rotates into the bottom of the cannon. As a result you can keep feeding the AC bullets without ever interrupting the action.
Knowing this you can keep an eye on your ammo count and keep on topping up your ammunition as you go. The animation to feed a clip takes less then a second.
Secondly helldivers have a magical flak ammo system. Where you can shoot out proximity granades that explode when it knows it is near something it can kill. Of course this is handy against shriekers. The flying bastards. But it functions well against all mid and low armour enemies. Shoot just above them and have the shrapnel rain on them. Shoot 5 shots in a row above a patrol and clear the hole things. It's basically an airburst rifle but when managing the ammo well doesn't take near the amount of time to reload.
As a result the AC can be very effective agains all grunts of the bugs as long as you can remember to never fire your last bullet and are capable of switching to FLAK ammo for a stalker as that is more likely to kill them in one shot then an APHET round. Learning to effectively learn how to use the autocannon against bugs has been a very rewarding experience and it's mostly because the devs have such a good attention to detail when it comes to the weapons action in this game.