When I started bowhunting I grunted or bleated every 15 minutes. To my knowlege I have never had a deer respond to a blind call (not counting rattling). I have not done that for several years, now I almost never blind call - simply because it seems a waste of time. If I hear or see deer I can be much more specific as to how I try to call them in - and I have had pretty good results that way.