Laser Bore Sighting an AR?

[gunblazar2]

Hope this isn't a dumb question.. I have a new M&P AR15 and tried to use a laser bore sight ar 15 to get my iron sights and optic close before going to the range. The boresight isn't giving me a distinct dot out of the barrel (just playing around at ~40-50ft), but rather a fist-sized, half moon blob. I thought maybe there was some fluff or dust in the barrel that was distorting the beam so I ran a bore snake thru it and the checked it with a flashlight. All clear. The boresight by itself does produce a distinct dot when handheld and aimed at the same spot. Is it possible the the rifling and shine of the never fired barrel is causing the laser to reflect, bounce around and distort? I've used boresights before with pistols with good results. But never tried it in a rifle. I did a search and got a few hits, but nothing specific to the issue I'm experiencing. Thanks in advance. Can't wait to get to the range with this thing to the range!