Gun beam lagging behind, how can I fix this?

Evening.

I have scripted a few guns in the past and they've all had this problem, and I'm thinking it's about time I ask for some help with it.

The gun is set up as one local script and two server scripts. The local script is firing a remoteEvent every time the gun is meant to fire (when the player clicks or every .5 seconds when the player is holding button1 down), with the mouse.hit of the player's mouse. One server scripts is for the beam, and the other is for damage. I will only include the local script and the beam server script here.

I have copied some of the code from developer.roblox.com, as I am too lazy to script it myself and I wouldn't have come up with anything different.

The beam server script creates a ray that extends for 300 studs when the server is fired. It then finds a part on this ray via workspace:FindPartOnRay() and takes the part and the position of the part as variables (part, position). It then creates a beam in the middle of the ray and sizes it to fit the ray's size (0.3, 0.3, distance/2). This beam, however, is lagging behind, which is incredibly frustrating.

The problem is not that the beam is spawning in the right place and the player is moving past it. The problem is that the beam is spawning behind where it should be, or where it would have been had the player fired a bit earlier. AKA the beam is lagging.

The local script:

--VARIABLES
local t = script.Parent.Parent
local ANIMS = t.ANIMS
local p = game.Players.LocalPlayer
local event = t:WaitForChild("Event")
local mouse = p:GetMouse()
local uis = game:GetService("UserInputService")

repeat wait() until p.Character
repeat wait() until p.Character.Humanoid

local c = p.Character
local h = c.Humanoid

local e = false
local patroltoggle = false
local debounce = false
local w = h.WalkSpeed

--ANIMATIONS
local idle = ANIMS.IDLE
idle = h:LoadAnimation(idle)
local patrol = ANIMS.PATROL
patrol = h:LoadAnimation(patrol)
local firing = ANIMS.FIRING
firing = h:LoadAnimation(firing)

local animations = {idle, patrol, firing}

--FUNCTIONS
local function stopAllAnims()
	for _, anim in pairs(animations) do
		anim:Stop()
	end
end

t.Equipped:Connect(function()
	e = true
	w = h.WalkSpeed
	idle:Play()
end)

t.Unequipped:Connect(function()
	e = false
	stopAllAnims()
end)

--MAIN FUNCTION
uis.InputBegan:Connect(function(input)
	if e == false then return end
	if debounce then return end
	
	--Firing
	if uis:IsMouseButtonPressed(Enum.UserInputType.MouseButton1) then
		patroltoggle = false
		patrol:Stop()
		h.WalkSpeed = w
		firing:Play()
		debounce = true
		wait(0.1)
		while uis:IsMouseButtonPressed(Enum.UserInputType.MouseButton1) do
			event:FireServer(mouse.hit)
			wait(0.5)
		end
		firing:Stop()
		debounce = false
	end

	--Running
	if input.KeyCode == Enum.KeyCode.F then
		if patroltoggle == false then
			patrol:Play()
			idle:Stop()
			h.WalkSpeed = w*2
			patroltoggle = true
		else
			patrol:Stop()
			idle:Play()
			h.WalkSpeed = w
			patroltoggle = false
		end
	end
end)

The beam server script:

--VARIABLES
local t = script.Parent.Parent
local event = t:WaitForChild("Event")

--MAIN FUNCTION
event.OnServerEvent:Connect(function(p, ...)
	local tuple = {...}

	--Creating ray
	local ray = Ray.new(t.Nozzle.Position, (tuple[1].p - t.Nozzle.Position).unit * 300)
	local part, position = workspace:FindPartOnRay(ray, p.Character, false, true)
	
	--Creating beam
	local beam = Instance.new("Part", workspace)
	
	beam.BrickColor = BrickColor.new("Toothpaste")
	beam.FormFactor = "Custom"
	beam.Material = "Neon"
	beam.Transparency = 0.25
	beam.Anchored = true
	beam.Locked = true
	beam.CanCollide = false
	
	--Positioning and sizing beam
	local distance = (t.Nozzle.CFrame.p - position).magnitude
	beam.Size = Vector3.new(0.3, 0.3, distance)
	beam.CFrame = CFrame.new(t.Nozzle.CFrame.p, position) * CFrame.new(0, 0, -distance / 2)
	
	--Deleting the beam
	game:GetService("Debris"):AddItem(beam, 0.1)
end)

If any more information is needed, this article should suffice, however feel free to comment with your questions.

ROBLOX Developer Website, Making a Laser Gun: https://developer.roblox.com/en-us/articles/Making-a-ray-casting-laser-gun-in-Roblox

When you make things that the client directly interacts with such as in your case guns, the most common method of doing so is to split up the special look effects from the real effects.

What I mean by this, is you want to show the beam through the client's script, but do your calculations if it hit anything on the server script. This will ensure that the client doesn't experience any latency or delay in their interactions, but also that there isn't any way they can cheat the system because all your important calculations are on the server.

Here is a very simple example...

Client

local UserInputService = game:GetService("UserInputService")

local player = game.Players.LocalPlayer
local mouse = player:GetMouse()

local Remotes = game.ReplicatedStorage.Remotes
local gunFired = Remotes:WaitForChild("gunFired")

local onCooldown = false

function cooldown()
	onCooldown = true
	wait(0.5)
	onCooldown = false
end

UserInputService.InputBegan:Connect(function(input, gameEvent)
	if not gameEvent then
		if input.UserInputType == Enum.UserInputType.MouseButton1 then
			if not onCooldown then
				createRay(mouse.Hit)
				-- If you need to be very accurate you can use 'tick()' to account for how much time it took for the server to get your request
				gunFired:FireServer(mouse.Hit, tick())
				cooldown()
			end
		end
	end
end)

Server

local Remotes = game.ReplicatedStorage.Remotes
local gunFired = Remotes:WaitForChild("gunFired")

local onCooldown = false

function cooldown()
	onCooldown = true
	wait(0.5)
	onCooldown = false
end
gunFired.OnServerEvent:Connect(function(client, hit, t)
	if not onCooldown then
		local dt = tick() - t
		gunFired:FireAllClients(client, hit, t)
		processRay(hit, t)	-- For this ray you wouldn't show it, it would just be for determining if you actually hit something
		cooldown()
	end
end)

Other Clients

local UserInputService = game:GetService("UserInputService")

local player = game.Players.LocalPlayer
local mouse = player:GetMouse()

local Remotes = game.ReplicatedStorage.Remotes
local gunFired = Remotes:WaitForChild("gunFired")

gunFired.OnClientEvent:Connect(function(exclude, hit, t)
	local dt = tick() - t
	if player ~= exclude then
		createRay(hit, t)
	end
end)