I want to get a laser/tactical light to go on my new AR carbine.  Is it a good idea to mount those to the barrel?  

I can't afford the surefire laser, so it looks like Beamshot is the way i will go.  any help appreciated.

I have a Surefire tactical light mounted to the barrel of my LE M4 and it works great.  You will need to resight the weapon but it should only be a few clicks of elevation difference.  I have had 2 AR's with the tactical light mounted to the barrel and my Department has about a dozen of them mounted and they all work fine.  Just make sure you Loctite the barrel clamp screws or the thing will slide down the barrel after you shoot awhile.