Explosives are unlocked with just automation science. Craftable without oil thanks to Sulfur Deposits.
All bullet-type ammunitions require some amount of explosives to craft.

Throw explosives like a grenade, with high explosion damage over a smaller area.
Entities (chests, assemblers, vehicles, etc) with 12+ explosives inside will explode on death, equal to artillery explosion. This destroys cliffs.

Larger explosions are layered so damage falls off more gradually.
Grenade does physical damage via shrapnel.

Early firearm damage is more devastating
Firearms take time to reload (change magazine).
Reload early with CTRL+SPACE, leaving partial magazine on the ground.

Gun turret uses unique ammo: medium-caliber autocannon rounds.
Turrets take loose rounds with no magazine, requiring no reload time.