I picked up a Brunswick black diamond yesterday that is undrilled which is kinda of unusual, just wondering if this ball is valueable or just a old rubber ball serial number is 13D919?

Hard rubber balls are a lot like very very hard pure urethane balls.  I actually liked them as a niche ball up till a few years ago, but the oils have gotten so much heavier in both viscosity and volume, that you can hardly use one anymore unless the track is totally burned from the dots on down. 

Id actually be interested in it to be my spare ball. Id be worried about the weight being closer to 16lbs then 15.