Try placing more weight of the bowling ball on the base of the index finger and feeling it there throughout the swing, trying to keep more weight on the outside of your hand. Then at the bottom or the release try and feel your ring finger through the rotation.
Not knowing what your thumb pitches may be, you can go with away from the palm to get it off your hand earlier enhancing the quickness of the rotation.
Hope this makes sense.
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The views and opinions expressed by myself are solely those of mine and NO one else, nor are they affiliated with anyone else.

Take a foottball, underhand it for as long as it takes you to do a bowling ball the same way. It took me a month before I was comfortable with it.Pot bowled Sunday had my first 800. I had the beat pin action of my life.I think adding tilt to my game was the reason. If you learn it, your game will be more varied,pin action increases,scores will jump thru the roof. Good luck.
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Live free or die trying.

Doug,
 I've read in your profile that your speed is 18 mph @ the pins,that equals about 20 off the hand? have you tried to slow the ball speed down to give your hand time to come around the ball? I know when I throw that fast the only way I can rev it is straight up the back,don't have time in my release to come around the ball.if I slow it down I have all kinds of time and feel to turn the ball more and it creates more skid and hook on the back end,just a thought.
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The harder I try the harder they fall

Lots of good info here:

http://www.bowl4fun.com/ron/roncarchive.htm

Tips 27, and 35-38 may be especially helpful.

Thanks for posting the link.  Ron C's tips are great!  I usually forget about his site most of the time, but it's great for a refresher or if in a slump.  Think I'll pass it on to a couple of the newer bowlers on our team since they're looking to improve.