Bullet Demo

-- To be used with the quickscripts plugin https://www.roblox.com/library/5602756723/QuickScript

local BulletSpeed = 300 -- Feet per second, 300 is around the speed of a paintball, 900 is around the speed of a handgun
local SimulationSpeed = 1 -- How fast time moves, Example; SimulationSpeed = 1/10 would make time flow 10 times slower
local Gravity = 20 -- How much to accellerate bullets downwards, 1 gravity means Velocity.Y increases by -1 every second

local TestKey
local Bullets = {}

local SpawnBullet = function(Origin, Direction, Speed)
    local BulletData = {
        Position = Origin;
        Velocity = Direction.Unit * Speed;
        LastPosition = nil;
    }

    local raycastParams = RaycastParams.new()
    raycastParams.FilterType = Enum.RaycastFilterType.Blacklist
    raycastParams.FilterDescendantsInstances = {workspace.Bullets, workspace.Hits}
    BulletData.raycastParams = raycastParams

    local BulletPart = Instance.new("Part", workspace.Bullets)
    BulletPart.Name = "BulletPart"
    BulletPart.Size = Vector3.new(.45,.45,.45)
    BulletPart.Color = Color3.new(1,1,0)
    BulletPart.Anchored = true

    BulletData.Part = BulletPart

    Bullets[BulletData] = true

    return BulletData
end

local DeleteBullet = function(BulletData)
    repeat
        BulletData.Part:Destroy()
    until BulletData.Part.Parent == nil or _G.TestKey ~= TestKey
    Bullets[BulletData] = nil
end

local UpdateBullet = function(BulletData, Delta)
    BulletData.Velocity = BulletData.Velocity - Vector3.new(0,Gravity,0)*Delta

    BulletData.LastPosition = BulletData.Position
    BulletData.Position = BulletData.Position + BulletData.Velocity * (Delta or 1)

    local Difference = BulletData.Position - BulletData.LastPosition
    local Distance = Difference.magnitude

    BulletData.Part.Size = Vector3.new(0.2, 0.2, math.max(Distance,0.2))
    BulletData.Part.CFrame = CFrame.new(BulletData.Position, BulletData.LastPosition)
    *CFrame.new(0,0,-BulletData.Part.Size.Z/2)

    local rayOrigin = BulletData.LastPosition
    local rayDirection = BulletData.Position - BulletData.LastPosition

    local raycastResult = workspace:Raycast(rayOrigin, rayDirection, BulletData.raycastParams)

    if raycastResult then
        local Marker = Instance.new("Part")
        Marker.Size = Vector3.new(.4,.4,.2)
        Marker.CFrame = CFrame.new(raycastResult.Position, raycastResult.Position + raycastResult.Normal)
        Marker.Color = Color3.new(0.1,0.1,0.1)
        Marker.Parent = workspace.Hits

        DeleteBullet(BulletData)
    elseif BulletData.Position.Y < -100 then
        DeleteBullet(BulletData)
    end

    return raycastResult
end

return function(QuickScripts)
    repeat
        TestKey = math.random(1,1000000)
    until TestKey ~= _G.TestKey
    _G.TestKey = TestKey

    if not workspace:FindFirstChild("Bullets") then
        Instance.new("Model",workspace).Name = "Bullets"
    end

    if not workspace:FindFirstChild("Hits") then
        Instance.new("Model",workspace).Name = "Hits"
    end

    workspace.Bullets:ClearAllChildren()
    workspace.Hits:ClearAllChildren()

    local plugin = QuickScripts.plugin
    plugin:Activate(true)

    local Mouse = plugin:GetMouse()

    local BulletShooter = Mouse.Button1Down:connect(function(k)
        local Camera = workspace.CurrentCamera
        SpawnBullet(Camera.CFrame.p-Vector3.new(0,1,0), Camera.CFrame.LookVector, BulletSpeed)
    end)

    local BulletUpdater;BulletUpdater = game:GetService("RunService").RenderStepped:connect(function(Delta)
        if _G.TestKey ~= TestKey then
            BulletUpdater:disconnect()
            BulletShooter:disconnect()
            return
        end

        for BulletData in pairs(Bullets) do
            UpdateBullet(BulletData, Delta * SimulationSpeed)
        end
    end)
end