That's what the "numbering system" is supposed to do for customers. Here is an example of how it was explained to me.
The first number (like the 5 in the 505A) supposedly denotes the performance level. With three levels originally (5's, 7's, and 9's). Since then, they have added a 6 series, a 3 series, and a 1 series, with the 1 series ball being a polyester spare ball, a 100P. (P is for Polyester)
The next two numbers (like the 05 in the 505A) supposedly denotes the core strength, with higher numbers equaling stronger cores.
The letter at the end (like the A in the 505A) originally denoted the type of reaction you could expect from the ball, with A meaning ANGULAR, C meaning CONTROL, and T meaning TRACTION.
The C was later said to mean CONTINUATION on the 919C, and the AT on the 916AT was said to mean ALL TERRAIN. They also produced one 6 series ball, the 607A SE, with the SE meaning Special Edition.
SO, given all of this, it boils down to this. An entry level ball (a 500 series ball) SHOULD be outperformed by ANY of the higher level balls with similar core numbers, a 700 series ball SHOULD outperform everything EXCEPT the 900 series balls.
To build an arsenal, this would give you several options. If you like the 505A, and just wanted something for more oil, you could either go to a 505T (for added traction), or a 718A to keep the sharp movement while still handling more oil.
Problem is, their nice, neat little system doesn't always work. The 505T was a strong piece, and performed better than some of the higher rated balls. OOOPS.
There are some really good guys here in the Track forum that are helpful many times. Hang in there, don't be shy, and ask LOTS of questions. There are those who will answer and be glad to help.
Edited by The Bowling Pariah on 8/5/2011 at 11:11 PM