I'm trying to figure out a few things about a gun turret. Can someone help me?

I'm making a gun turret to practice my raycasting abilities, and I am following a tutorial, but I have a problem. A few, actually. First, and biggest, in the findTarget function the script generates a ray, and multiplies it by 500 with a .Unit . What does that do? Second, I want to use that ray to make sure that its not firing at a wall the humanoid is hiding behind, but instead, the humanoid itself. Third, how would I add inaccuracy to my gun? Fourth, the FireBullet() function works, but how do I make the sound sound like its overlapping, it doesn't sound right, its sounds glitchy. Heres the code:

gun = script.Parent

function FindTarget()
	local dist = 100
	local target = nil
	for i,v in pairs(workspace:GetChildren()) do
		local torso = v:FindFirstChild("Torso")
		local humanoid = v:FindFirstChild("Humanoid")
		if torso and humanoid and humanoid.Health > 0 then
			if (gun.Position - torso.Position).magnitude < dist then
				local ray = Ray.new(gun.Position, (gun.Position- torso.Position).Unit*500)
				local hit,position = workspace:FindPartOnRayWithIgnoreList(ray,{torso.Parent})
				if hit == nil then
					dist = (gun.Position - torso.Position).magnitude
					target = torso
				else
					print(hit.Name)
				end
				dist = (gun.Position - torso.Position)
				target = torso
			end
		end
	end
	return target
end

function FireBullet()
	s = workspace.Sound:Clone()
	s.Parent = script.Parent
	s:Play()
	wait(0.6)
	s:Destroy()
end

while wait(0.3) do
	local torso = FindTarget()
	if torso then
		gun.CFrame = CFrame.new(gun.Position, torso.Position)
		local b = Instance.new("Part",workspace)
		b.Size = Vector3.new(0.2,0.2,1)
		b.BrickColor = BrickColor.new("New Yeller")
		b.Velocity = gun.CFrame.lookVector*500
		b.CFrame = gun.CFrame + Vector3.new(0.2,0.2,0.2)
		b.Touched:connect(function(obj)
		FireBullet()
			local human =  obj.Parent:FindFirstChild("Humanoid")
			if human then
				human:TakeDamage(5)
			end
			if obj ~= gun then
				game:GetService("Debris"):AddItem(b,0)
			end
		end)
	end
end

I believe your problem is..

.~~~~~~~~~~~~~~~~~ for i,v in pairs(workspace:GetChildren()) do

I believe its this because not everything in the workspace may have a child 'Humanoid' which will trigger an error that will discontinue the code.

You can use a pcall function or make it simple... But it will only work on Players

for i, v in pairs(game.Players:GetPlayers()) do
	wait()

	local Character = v.Character
end

Another reason it may be breaking when player character code runs the player isn't fully loaded...

for i,v in pairs(workspace:GetChildren()) do
	wait()
	--Code
end