Tutorial — Weapon with the Fire Component

Goal: give a character a weapon that fires Mass projectiles with a fire rate, spread and pellets, and that works unchanged in single-player and multiplayer.

Time: 15 minutes.

The Mass Projectile Fire component (UMassProjectileFireComponent) wraps the spawn call with:

• a fire-rate accumulator (Consume Fire Rounds),
• muzzle, pellet and spread settings,
• client prediction + a compact, validated server RPC when the owner is replicated,
• a preload of its projectile type on BeginPlay, so the first shot does not hitch.

#Part A — Minimal automatic weapon

#Step 1 — Add the component

Open your Character Blueprint → Components → Add → search Mass Projectile Fire.

Leave Component Replicates ticked for multiplayer.

#Step 2 — Trigger logic

In the Event Graph:

1. Fire Pressed → MassProjectileFire → Reset Fire Accumulator → Fire (Rounds = 1) → set bFiring = true.
2. Fire Released → set bFiring = false.
3. Event Tick → Branch bFiring → MassProjectileFire → Consume Fire Rounds (Delta Seconds) → if Return Value > 0 → Fire (Rounds = Return Value).

That's a complete automatic weapon. Fire aims along the controller's control rotation from Actor Location + Muzzle Offset.

#Step 3 — Aim from the camera or a muzzle socket

Replace Fire with Fire From, which takes an explicit world Origin and Direction:

• First-person: Origin = camera location + forward × 50, Direction = camera forward.
• Third-person: Origin = weapon mesh socket Muzzle, Direction = (crosshair trace hit − Origin), normalized.

#Part B — Real example: the Shooter template

This project's weapons (Epic's First Person template, Shooter variant) were converted to Mass projectiles like this.

1. The component lives on the character, not the weapon. Weapons are swapped at runtime, but the character is the replicated owner that can send server RPCs.

2. The weapon Blueprint finds it on its owner. In BP_ShooterWeaponBase → Fire Bullet: Get Owner → Get Component by Class (Mass Projectile Fire Component) → Cast To MassProjectileFireComponent.

3. It sets the type for this weapon and fires from the muzzle. Each weapon Blueprint has an instance-editable MassProjectileType variable (Rifle → EC_Projectile_Rifle, Pistol → EC_Projectile_Plasma, Grenade Launcher → EC_Projectile_Shell). The weapon Sets the component's Projectile Type and calls Fire From with the bullet spawn location and its forward vector.

4. Only the locally controlled copy fires. The weapon exists on every machine for animation and effects. Fire Bullet checks Is Locally Controlled on the pawn owner before calling the component, so a shot is sent exactly once. The component then handles prediction and the server RPC.

5. Fallback. If the cast fails (a weapon held by an actor without the component), the weapon calls Fire Projectiles directly with a Make Projectile Fire Event.

#What the component does in each net mode

Server-side validation (Project Settings → Networking):

• Pellets Per Shot × rounds in one call must be ≤ Max Net Projectiles Per Fire Event (256), or the client is disconnected. Keep Consume Fire Rounds' Max Rounds This Frame (default 32) × pellets under that limit.
• More than Max Net Fire Events Per Second Per Player (200) RPCs per second are dropped.
• Muzzles farther than Max Net Fire Origin Distance Cm (30 m) from the pawn are dropped.

Dropped shots exist only on the firing client, and the log shows ServerFire dropped (<reason>).

#Node reference