The following support gems are recommendations by GGG as listed in-game, and do not necessarily reflect optimal combinations or the views of the wiki.
Gem tier
Support gems
I
Ammo ConservationAmmo ConservationTier: 1 Level: 1Supported crossbow attacks have 25% chance to not consume a boltSupports Crossbow Ammunition Skills, granting a chance to not consume a Bolt when firing.Place into a Skill's Support Gem socket in the Skills Panel to apply its effects to that Skill. You cannot have multiple copies of the same Support Gem socketed at the same time.
Lightning InfusionLightning InfusionAttack, Lightning Tier: 1 Level: 1Supports Attacks, causing them to Gain Cold Damage but deal less Fire and Lightning DamageSupported Attacks Gain 25% of Damage as extra Lightning Damage Supported Attacks deal 50% less Cold and Fire DamagePlace into a Skill's Support Gem socket in the Skills Panel to apply its effects to that Skill. You cannot have multiple copies of the same Support Gem socketed at the same time.
Martial TempoMartial TempoAttack Tier: 1 Level: 1Supports Attacks, causing them Attack faster.Supported Skills have 25% more Attack SpeedPlace into a Skill's Support Gem socket in the Skills Panel to apply its effects to that Skill. You cannot have multiple copies of the same Support Gem socketed at the same time.
II
Fresh ClipFresh ClipTier: 2 Level: 1Supports Crossbow Skills, granting them more damage for each bolt reloaded by that Skill in the last 6 secondsSupported Crossbow Skills deal 1% more Damage for each bolt Reloaded by that skill in the past 6 secondsPlace into a Skill's Support Gem socket in the Skills Panel to apply its effects to that Skill. You cannot have multiple copies of the same Support Gem socketed at the same time.
MaimMaimAttack Tier: 2 Level: 1Supports Attacks, causing them to Maim enemies.Supported Attacks always Maim on HitPlace into a Skill's Support Gem socket in the Skills Panel to apply its effects to that Skill. You cannot have multiple copies of the same Support Gem socketed at the same time.
Primal ArmamentPrimal ArmamentAttack Tier: 2 Level: 1 Cost & Reservation Multiplier: 120%Supports Attacks that use a weapon, causing them to deal more weapon Elemental damage.Supported Skills deal 25% more Weapon Elemental DamagePlace into a Skill's Support Gem socket in the Skills Panel to apply its effects to that Skill. You cannot have multiple copies of the same Support Gem socketed at the same time.
III
Elemental FocusElemental FocusTier: 3 Level: 1Supports any skill that Hits enemies, causing it to deal more Elemental Damage but be unable to inflict Elemental Ailments.Supported Skills deal 25% more Elemental Damage Supported Skills cannot inflict Elemental AilmentsPlace into a Skill's Support Gem socket in the Skills Panel to apply its effects to that Skill. You cannot have multiple copies of the same Support Gem socketed at the same time.
Neural OverloadNeural OverloadLightning Tier: 3 Level: 1 Cost & Reservation Multiplier: 120%Supports any skill that Hits enemies. Nearby enemies are marked when they are Primed for Electrocution, and hitting a marked enemy with a supported skill will Electrocute them.Supported Skills Electrocute Primed enemies on HitPlace into a Skill's Support Gem socket in the Skills Panel to apply its effects to that Skill. You cannot have multiple copies of the same Support Gem socketed at the same time.
Nimble ReloadNimble ReloadTier: 3 Level: 1Supports Crossbow Ammunition Skills, causing them to Reload bolts significantly faster.Supported Skills have 60% increased Crossbow Reload SpeedPlace into a Skill's Support Gem socket in the Skills Panel to apply its effects to that Skill. You cannot have multiple copies of the same Support Gem socketed at the same time.
Item acquisition
Shockburst Rounds has restrictions on where or how it can drop.