If you want to scare the bad guy, turn on all the lights and appear before him, stark naked. Or, get a big bad dog. Scaring with a gun is a bad idea, even with blanks.
Besides, why do you think the bad guy will be of the frame of mind to be scared. He very well may be some crackhead jonesing for a fix, somebody on PCP, or in some other deluded state where scare tactics are not going to work well. On top of that, when you do decide to shoot your blank round, you have given up your position and whatever element of surprise you might have had.
I think appearing before him naked is your best option for creating fright.
"If you look through your scope and see your shoe, aim higher."
-- said to me by my 11 year old daughter before going out for hogs 8/13/2011