It looks a lot like a glue failure. Is there any splintering, chunks of bow left on the riser, or chunks of riser left on the bow? It appears to be clean in the picture. It can still be caused by flex in the handle. Clean it really good. Then degrease it with acetone. Sand the handle area (on riser and bow) with 40 grit to rough it up to take the glue. Degrease it again, then do just like George said. If you watch the depth of the drill closely like George mentions, and adjust it every time, you can keep the drill from comming out the back of the bow and eliminate the possability of having a splinter rise. Drill from the riser to within 1/4" of the back but don't go all the way through. Glue the riser to the bow first so it will stay put while you drill. Justin