I bought a pair of LaserGuards, one for a Kahr, a LG-437 and one for my Glock a LG-436. I also ended up buying two Crossbreed SuperTucks designed to fit the guns with these lasers installed so I have a little invested in this laser system. The 437 has been perfect over several hundred rounds, maybe 400 but Crimson Trace is sending me my third 436. When I install the unit and it is tightened down the unit stops working. When I take it off of the gun and tighten it down the unit stops working. Somehow the screws are either shorting out the circuit or pushing the battery out of contact somehow. Anyone else have this problem with a LaserGuard on a Glock. Note, that Crimson Trace is taking very good care of me. They replaced this first one right away and the replacement for the second one is being overnighted. They are not balking about replacing them. Both units are relatively new production in that the first unit was made in Dec 2010 and the second unit was made in Feb 2011. Any ideas?