How to fix my raycasting system for my turret?

Kinda sounds like your targeting code is getting confused with things in the workspace.

try this code:

local RS = game:GetService("ReplicatedStorage")
local bullet = RS:WaitForChild("Bullet")

local Turret = script.Parent

local fireRate = 1


local Damage = 20
local bulletSpeed = 250
local detectDistance = 50

--// new function for handling the targeting code. This simply finds the Closest humanoid in the workspace
function getHumanoidTarget()
    local target = nil
    local Dist = detectDistance 
    for k,v in pairs(workspace:GetChildren()) do -- replace workspace:GetChildren() with workspace:GetDescendants() for a more full but slow search 
        local Humanoid = v:FindFirstChildOfClass("Humanoid")
        local Torso = v:FindFirstChild("Torso") or v:FindFirstChild("HumanoidRootPart")
        if(Humanoid ~= nil and Humanoid.Health > 0 and Torso ~= nil) then
            local dist = (Torso.Position - Turret.Position).magnitude
            if(dist < Dist) then
                Dist = dist
                target = v
            end
        end
    end
    return target
end

while wait(fireRate) do

    local target = nil
    local tgt = getHumanoidTarget() -- Call our new Targeting function
    if(tgt ~= nil) then -- we've got a target!
        local torso = tgt:FindFirstChild("Torso") or tgt:FindFirstChild("HumanoidRootPart")
        if(torso ~= nil) then -- It has a torso or HumanoidRootPart!
        if (torso.Position - Turret.Position).magnitude <= detectDistance then -- woot we can see it!
            local raycastParams = RaycastParams.new()
            raycastParams.FilterDescendantsInstances = {workspace.Turret}
            raycastParams.FilterType = Enum.RaycastFilterType.Blacklist

            local BulletPathResult = workspace:Raycast(Turret.Position,(torso.Position - Turret.Position).Unit*detectDistance, raycastParams)

            -- Problem begins here -- should be fixed!
                if BulletPathResult.Instance == torso 
                    or BulletPathResult.Instance.Parent:FindFirstChild(torso.Name) then -- remove this bit to make it less precise in targeting 
                print("Targeting the humanoid")
                    target = torso
            else 
                target = nil
                print("Object is in the way")
            end
            --problem ends here
        end
        end
        if target then
            local torso = target

            Turret.CFrame = CFrame.new(Turret.Position, torso.Position)

            print("Fire")
            local bulletClone = bullet:Clone()
            bulletClone.Parent = game.Workspace
            bulletClone.Position = Turret.Position
            bulletClone.Velocity = Turret.CFrame.LookVector * bulletSpeed
            bulletClone.Touched:Connect(function(hit)
                local human = hit.Parent:FindFirstChild("Humanoid")
                if human then
                    human:TakeDamage(Damage)
                    bulletClone:Destroy() -- Had to add this here as it would instantly kill you lolz
                end
                wait(3)
                bulletClone:Destroy()
            end)
        end
    end
end

a remix of your turret code to follow the target humanoid when it "sees it" :)

Integrated FPS code used for the Firing sequence, Since this code is running every game tick!.

Make the turret Follow you and fire code:

local RS = game:GetService("ReplicatedStorage")
local bullet = RS:WaitForChild("Bullet")

local Turret = script.Parent

local fireRate = 1


local Damage = 20
local bulletSpeed = 250
local detectDistance = 50


function getHumanoidTarget()
    local target = nil
    local Dist = detectDistance 
    for k,v in pairs(workspace:GetChildren()) do
        local Humanoid = v:FindFirstChildOfClass("Humanoid")
        local Torso = v:FindFirstChild("Torso") or v:FindFirstChild("HumanoidRootPart")
        if(Humanoid ~= nil and Humanoid.Health > 0 and Torso ~= nil) then
            local dist = (Torso.Position - Turret.Position).magnitude
            if(dist < Dist) then
                Dist = dist
                target = v
            end
        end
    end
    return target
end

local t = 0

local FPS = 0
local time = tick()


while true do
    --// FPS Code 
    local NowTime = tick()
    local dt = NowTime - time
    time = tick()

    local FPS = (1/dt) -- the frames per second we're running at!
    --// End of FPS Code


    local target = nil
    local tgt = getHumanoidTarget()
    if(tgt ~= nil) then
        local torso = tgt:FindFirstChild("Torso") or tgt:FindFirstChild("HumanoidRootPart")
        if(torso ~= nil) then
        if (torso.Position - Turret.Position).magnitude <= detectDistance then
            local raycastParams = RaycastParams.new()
            raycastParams.FilterDescendantsInstances = {workspace.Turret}
            raycastParams.FilterType = Enum.RaycastFilterType.Blacklist

            local BulletPathResult = workspace:Raycast(Turret.Position,(torso.Position - Turret.Position).Unit*detectDistance, raycastParams)

            -- Problem begins here -- should be fixed!
                if BulletPathResult.Instance == torso 
                    or BulletPathResult.Instance.Parent:FindFirstChild(torso.Name) then
                print("Targeting the humanoid")
                    target = torso
            else 
                target = nil
                print("Object is in the way")
            end
            --problem ends here
        end
        end
        if target then
            local torso = target

            Turret.CFrame = CFrame.new(Turret.Position, torso.Position)
            if(t%math.floor((fireRate*FPS) +0.5) == 0) then -- fire according to fireRate * FPS 
                print("Fire")
                local bulletClone = bullet:Clone()
                bulletClone.Parent = game.Workspace
                bulletClone.Position = Turret.Position

                bulletClone.Velocity = Turret.CFrame.LookVector * bulletSpeed

                bulletClone.Touched:Connect(function(hit)
                    local human = hit.Parent:FindFirstChild("Humanoid")
                    if human then
                        human:TakeDamage(Damage)
                        bulletClone:Destroy()
                    end
                    wait(3)
                    bulletClone:Destroy()
                end)
            end
        end
    end
    wait()
    -- advance time by 1 tick...
    t = t +1
end