Ammo crafting

Horizon features an ammo crafting system, which uses the Weapons Lab.

Obtaining ingredients
Ammo is crafted from one of main materials (Explosive Material, Smokeless Powder, Energy Cells). Best way to get them as of 1.7.6 appears to be deploying a lot of entertainer Settler Mission and use the caps to buy bulk materials from merchants, like Ronnie Shaw or upgraded settlement ones. They also can be obtained via Militia (Settler Mission) or disassembly of unneeded ammo. Materials often can be traded for other materials in Market Trading Terminal.

Cryo

 * Freezing effects from the Cryolator or Cryo Rounds, now work on most enemies (to varying degrees)
 * Consecutive hits on tougher enemies, only partially chill them, and still cannot completely freeze them
 * Consecutive hits on weaker enemies can still freeze them solid as usual
 * Some creatures now have Cryo Resistance
 * Creatures that have Cryo Resistance, are often susceptible to taking extra fire damage (useful when using Awareness)

Armor piercing incendiary

 * There is no more armor penetration on perks and weapon receivers, its only based on the ammo now
 * API Rounds loaded into weapons will grant armor penetration based on the weapon and the caliber
 * .50 API = -100% Armor Penetration
 * .308 API = -85% Armor Penetration
 * .45 API = -50% Armor Penetration
 * 5.56 API = -50% Armor Penetration
 * Some API rounds can shoot through walls and body parts based on the weapon and the caliber
 * Lower caliber rounds have a lower hit chance in VATS to hit through walls and body parts
 * All API rounds are now more expensive to craft, and require Tungsten alloy
 * There are more sources of Tungsten alloy in loot/junk now
 * Tungsten Rod (junk): scraps into 2 tungsten alloy (located rarely on some vendors or loot)

High-explosive

 * These rounds explode on contact damaging everything in a small area for 20 damage per hit
 * These rounds have a 20% chance of knocking down the main target you hit directly
 * The knockdown effect does not work on larger enemies
 * These rounds do not pierce armor (they do not have the internal mechanics that API rounds have to penetrate armor, only raw explosive material)
 * HE rounds are only available on weapons that use .50 and 12.7mm

Irradiated Rounds

 * Adds radiation damage, but reduces ballistic damage
 * Irradiated rounds are only available on weapons that use .38 rounds

Pulse Rounds

 * Adds energy damage, but reduces ballistic damage
 * Deals +50% damage against Robots and Synths
 * Pulse rounds are only available on weapons that use .44 rounds
 * Has a graphical EMP effect upon impact

VENOM Rounds

 * Adds 40 poison damage over 10 seconds, but reduces ballistic damage
 * VENOM rounds are only available on weapons that use .44 rounds
 * Has a graphical green cloud effect upon impact