Can't accurately predict raycast trajectory

[LittleBagOfGarbage (joe)]

I was trying to make a gun from scratch and started simple by using a raycast for the bullet trajectory. I also wrote a function that SHOULD accurately draw the bullet path, but something here isn’t quite working as it should…

local tool = script.Parent
local gun = tool.Handle

local RAYCAST_LENGTH = 100
local DAMAGE = 10

local function DrawLine(A,B,color)
	local line = Instance.new("Part")
	line.Parent = workspace
	line.CanCollide = false
	line.Anchored = true
	line.CastShadow = false
	line.BrickColor = color
	
	local Center = (A + B) / 2
	line.CFrame = CFrame.new(Center, A)
	line.Size = Vector3.new(0.1,0.1,(A-B).Magnitude)
	
	task.spawn(function()
		while task.wait() do
			line.Transparency += .01
			if line.Transparency >= 1 then
				line:Destroy()
				break
			end
		end
	end)
end

local function onActivate()
	local direction = gun.CFrame.LookVector
	
	local distance = direction * RAYCAST_LENGTH
	local origin = gun.Attachment.WorldCFrame.Position --attachment is aligned with end of barrel
	
	DrawLine(origin,distance,BrickColor.Red())
	
	local bullet = workspace:Raycast(origin,distance)
	if bullet then
		DrawLine(origin,bullet.Position,BrickColor.Green())
		if bullet.Instance.Parent:FindFirstChildWhichIsA("Humanoid") then
			bullet.Instance.Parent:FindFirstChildWhichIsA("Humanoid").Health -= DAMAGE
		end
	end
end

I’ve inserted the DrawLine function at two points: one that predicts the bullet trajectory (colored red) and one that traces the ‘actual’ bullet trajectory based on the raycast results (green). This is what it looks like when I fire the gun:

For some reason the red line is always crooked no matter what. Since the green line is always straight I assume the issue isn’t with the DrawLine function but everything else seems perfectly fine. What exactly am I doing wrong here?

Also not super related but the green line only appears sometimes, even if the raycast would have clearly hit something right in front of it.

[2049_dev]

print distance and bullet.Position and compare , then print direction ,maybe the problem is from there

[LittleBagOfGarbage (joe)]

Sorry I should have been more clear in my post - I know that the destination or ‘point B’ is the issue here, but I have zero idea how to fix it. I’m terrible at vector math. Clearly I’m not recreating the raycast correctly but I don’t know why it doesn’t work.

[Riesegarder]

DrawLine(origin,distance,BrickColor.Red())

Your DrawLine function expects a Vector3 position for the second argument. You’re passing in distance, which is a direction vector. While technically they’re both Vector3s, in context they’re quite different. bullet.Position is a position vector relative to workspace origin, while distance is derived from the gun’s lookVector, which is a unit vector used to denote direction.

It should be:
DrawLine(origin, origin + distance, BrickColor.Red())