This question appears to be asked again and again on BowlingChat.net. If you don’t know anything about the Dual Angle Layout Technique, please feel free to read the introductory pieces I wrote on it’s use and application.
The Dual Angle Layout Technique uses two angles relative to a line from the Pin to the PAP. The Drilling angle angle is the angle from the PSA. However, Symmetric balls do not have a PSA undrilled, so we use a line through the CG instead. This creates an imaginary drilling angle for use whilst creating a layout.
Unlike asymmetric balls which show very little movement in the PSA between the undrilled and drilled ball, in symmetric balls the PSA will end up in or very near the center of the thumb hole. What this means, is the intended drilling angle and the actual drilling angle will be quite different. This leads to an obvious question – do the drilling angles actually mean anything on a symmetrical ball?
In short: NOTHING! If we take three symmetrical balls with the same pin out and top weight and apply layouts with the same Pin to PAP and VAL angle, but differing drilling angles, we will get the same reaction, or as close as is possible between three balls. The reason for this is obvious – the actual drilling angles on each ball will be pretty much identical, since the PSA will end up in thumb hole.
So what is the purpose of the drilling on symmetric balls if the play little role in the final ball motion? We use it to position our CG to allow the use of certain weight hole positions. As it turns out, when we place a weight hole, the PSA will move toward that hole, thus changing the drilling angle yet again. A well placed weight hole will actually make the final drilling angle MUCH closer to the intended drilling angle!
So do drilling angles matter on symmetric equipment? The intended drilling angles, not so much, but the actual drilling angles are just as important as they are on asymmetrical balls.