Wasn't sure where to post this so I thought it'd fit best here. I'm running into a problem where the power tool junkie in me can't find a suitable alternative.

I'm installing quite a few doors in my basement and can't figure out the best method to mortise for the strike plates. The corners need to be rounded and I don't have a round chisel. Since the door frames are already installed, routing them out isn't an option.

How does everyone else cut the rounded corner mortises? I've tried scoring the line with a utility knife but my skill/technique ends up with a very jagged looking curve.

Thanks in advance,
Wes