I'll get with my driller over the spring/summer on this issue but wanted to bounce an idea off the fine folks at BR.

I'm thinking I need a little more forward pitch.  All things being equal and my thumb fitting straight in the ball will always be cocked forward towards the finger holes.

I get a little rub and callous at the base of the inside of my thumb because of it and to feel secure end up grabbing the ball. I notice when I do this I'm pressing the back of my thumb up against the hole and my thumb is no longer straight in the ball.

It's starting to affect my spare shooting as well as I'll either try to relax the hand and dump it right or hold on and miss left.

Any thoughts?  I have an old ball I'm going to be plugging and drilling all Summer till this is fixed!

Oh my lord!
http://www.ballreviews.com/miscellaneous/brcom-unofficial-faq-section-repost-t74110.0.html

Section on thumb pitch...may help.

Ooops, seems to have been edited out.

Thumb pitch does not exist in a vacumm.  Bill Taylor postulated it had to do with a 64 degree angle between the thumb and the fingers.

This meant his forward reverse pitch table was set at 0 degrees for a standard flexibility and length thumb at 4 1/4 inches span, this was 64 degrees.
Everything longer in span called for more reverse to maintain the 64 degree angle, everything shorter called for going forward.

Adjustments were 1/16 adjusted pitch for every 1/8 longer or shorter span.

The table looked like this.
4 inch span = 1/8 forward thumb pitch
4 1/4 = 0 forward/reverse thumb
4 3/8 = 1/16 reverse
4 1/2 = 1/8 reverse
4 3/4 = 1/4 reverse
5 inch = 1/2 reverse.

Shorter, dryer, and more flexible thumbs often are about 1/8 forward of the table, longer, wetter, and stiffer thumbs are often about 1/8 reverse of the table.

Many feel the table to be slightly too far in reverse for today's bowling toss, I am almost dead on it except for a dryer slightly shorter thumb has me about 1/8 more forward of the table as to be expected!

REgards,

Luckylefty

Boss,

You mention rubbing under flat of thumb and callous.

This is usually indicative of not enough front of thumb bevel.  As you go forward without increasing bevel can result in worse and possible nerve damage which is exhibited by a black line under the front of thumb.  Also some sort of electric shock feeling.

Be careful of going forward without addressing this issue first.

I always mention to people that great bowling is usually indicated by a thumb release much earlier than the fingers.  The fingers then lift and rotate.  The best bowlers I see have a significant time difference in these two exits.

Good luck in finding your best release setup.

Regards,

Luckylefty
PS no matter what you do when the proper pitches are setup and the proper bevel and span, it feels like butter when coming out, and your hook and revs are all you will ever need when right.  Or as my Son says, "why bother with the thumb"!@  Those pesky two handers!

If you "cock" your thumb, the hole is too big and this causes a callous, usally on the back of the thumb. Like stated in previous post, there are a lot conditions to consider when pitching a thumb hole and a good driller will consider them all.

If you change your thumb pitches you also need to look at changing span/finger pitches as well.  They are all in direct correlation to each other.  I have played around with some different spans/pitches.  For myself I have found that I like a little forward 1/16 in my thumb but had to increase the away pitch in my fingers to adjust for my thumb now being slightly forward.  But I use switch grip and have different thumbs with different pitches based on how I am playing the lanes and what I want to do to the ball at that time.  The best thing you can do is go to a well respected pro shop near you and have him check everything out and try a few grips out. 

1/8th forward and 1/16th longer span and so far so good. Need a size smaller in inserts it turns out as well.

Just need to get the thumb hole right again but I am not squeezing at the moment.