Although the drill worked well, the chuck on my DeWalt hammer drill continued to loosen. I've been tightening the chuck like hell, but it's been loosening a lot (like 60 seconds of drilling). I have to admit that concrete is very strong, but I had better luck with the Bosch drill (see picture) which had an out-of-round shank. After about 20 minutes of drilling, the Bosch bit did not fall out of the drill chuck.