Issues with Raycasting; am I doing this right?

		local start = thisGun.Position
		local lookAt = thisGun.Position + thisGun.CFrame.lookVector*900
		--print("This gun is at position "..start.x..","..start.y..","..start.z)
		--print("Looking at position "..lookAt.x..","..lookAt.y..","..lookAt.z)
		local ray = Ray.new(start, (lookAt - start).unit)
		local targetHit, targetHitPos = game.Workspace:FindPartOnRay(ray)
		local targetHitName
		local mag = (thisGun.Position - targetHitPos).magnitude

		if targetHit ~= nil and mag < 1000 then
			targetHitName = targetHit.Name
		else
			targetHitName = "nil"
			targetPos = lookAt
			mag = (thisGun.Position - targetPos).magnitude
		end

This is the code I've currently got; the code which actually creates the raycasted line is later, and all works correctly; the issue I'm having is that targetHit and targetHitPos are always nil and the point that is 1 unit in front of the gun. Did I do something incorrect in creating the ray that is creating a ray with length of 1?

ROBLOX uses a weird definition of ray.

More accurately, Ray.new describes a segment of space -- from a particular point, to a particular point -- the ray stops after the length is done.

Since you are constructing it with a .unit vector, the Ray will only look 1 stud (the length of a unit vector) in that direction (and anything after it will pretend it doesn't hit).

Drop the .unit and that should work fine.

Style note:

local lookAt = thisGun.Position + thisGun.CFrame.lookVector*900

What you really mean with this line is

local lookAt = start + thisGun.CFrame.lookVector*900

This is better because you have to change less code if you tweak the start position; it also makes it clearer what you're doing, because later you use lookAt only as (lookAt - start).

Since you're only subtracting start after adding it, you might as well remove that and clean things up a bit:

local direction = thisGun.CFrame.lookVector

local ray = Ray.new(start,  direction.unit * 990 )
-- Only values up to 1000 work, but most of the time you want as long as possible