- Blue/Black Classic GL 4

First Impressions
The AMF Blue/Black Classic GL 4, released around 1991, is a typical representative of the late urethane era, one that remained in the lineup as a reliable option alongside the arrival of the first reactive balls (such as the Ninja). Visually, the ball comes in a marbled mix of black and blue, which gives it a more modern look compared to the mostly single-color urethane predecessors. The "GL 4" designation refers to AMF's performance ranking at the time (Guide Line), with the "4" standing for moderate hook potential. Technically, the ball is based on a robust urethane cover that was usually sanded to a matte finish out of the box in order to ensure solid traction. Inside works a traditional three-piece core (pancake style) or a very simple modified block, which results in a high RG and a low differential. That means: little flare and an extremely stable, quiet ball motion.
Comparison
Compared directly to the AMF Ninja (black version), which in the same period ushered in the era of high-performance bowling with more aggressive cores, the Classic GL 4 seems almost static. Where the Ninja reacts explosively at the breakpoint and practically plows through the pins, the GL 4 describes a gentle, almost lazy arc. Set against the reference ball of that time, the Faball Blue Hammer, the AMF Classic GL 4 often comes across as somewhat weaker at impact. Users reported back then that the Blue Hammer hit "harder" and mixed the pins better, while the GL 4 more often left solid corner pins (flat 10) on less-than-perfect pocket hits. It behaves more like a "diet" urethane ball: the same characteristics as the big boys (Angle, Hammer), but with less motor under the hood.
On the Lanes
From today's perspective, the AMF Blue/Black Classic GL 4 is a specialist for dry to very dry lanes. It's the ideal choice when modern urethane balls (like a Pitch Black) or weak reactive balls read too early and burn up energy. Thanks to its simple core, it largely ignores the friction in the heads and offers absolute control at the breakpoint. It doesn't jump, it doesn't dart — it rolls. That also makes it an excellent spare ball if you want a minimal amount of traction on your spare shots so you don't slide past "sleeper" pins, while still simulating the straight motion of a polyester ball. For the strike shot on normal house patterns, however, it simply lacks the carry potential these days.