The word Light on an old Hammer just meant that the ball had a pancake core instead of the original Hammer 2-piece core. The Blue Hammer was an agressive, strong urethane in its day, but its not very strong compared to the stuff that is currently available.
There are many suitable replacements available that will give the same type of reaction. These lines are very close: AMF Courage, Brunswick Groove, Columbia Scout, Ebonite Tornado, Storm Hit. The Blue Sanded Groove is probably the closest you can get--even the color is close.
Truth be told, at 10 lbs., unless its a polyester ball, you aren't going to find anything that's much different than the Blue Hammer.
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Good luck & good bowling