curve that allows them to smoothly feed ammunition into the chamber. Their heavy steel construction combined with "feed-lips" (the surfaces at the top of the magazine that control the angle at which the cartridge enters the chamber) machined from a single steel billet makes them highly resistant to damage. These magazines are so strong that "Soldiers have been known to use their mags as hammers, and even bottle openers". This contributes to the AK-47 magazine being more reliable, but makes it heavier than U.S. and NATO magazines. The early slab-sided steel AK-47 30-round detachable box magazines had sheet-metal bodies and weighed empty. The later steel AKM 30-round magazines had lighter sheet-metal bodies with prominent reinforcing ribs weighing empty. To further reduce weight, a lightweight magazine with an aluminum body with a prominent reinforcing waffle rib pattern weighing empty was developed for the AKM that proved to be too fragile and the small issued amount of these magazines was quickly withdrawn from service. As a replacement steel-reinforced 30-round plastic 7.62×39mm box magazines were introduced. These rust-colored magazines weigh empty and are often mistakenly identified as being made of Bakelite (a phenolic resin), but were actually fabricated from two-parts of AG-S4 molding compound (a glass-reinforced phenol-formaldehyde binder impregnated composite), assembled using an epoxy resin adhesive. Noted for their durability, these magazines did however compromise the rifle's camouflage and lacked the small horizontal reinforcing ribs running down both sides of the magazine body near the front that were added on all later plastic magazine generations. A second generation steel-reinforced dark-brown (color shades vary from maroon to plum to near black) 30-round 7.62×39mm magazine was introduced in the early 1980s, fabricated from ABS plastic. The third generation steel-reinforced 30-round 7.62×39mm magazine is similar to the second generation, but is darker colored and has a matte nonreflective surface finish. The current issue steel-reinforced matte true black nonreflective surface finished 7.62×39mm 30-round magazines, fabricated from ABS plastic weigh empty. Early steel AK-47 magazines are long; the later ribbed steel AKM and newer plastic 7.62×39mm magazines are about shorter. The transition from steel to mainly plastic magazines yields a significant weight reduction and allows a soldier to carry more ammunition for the same weight. All 7.62×39mm AK magazines are backwards compatible with older AK variants. 10.12 kg (22.3 lb) is the maximum amount of ammo that the average soldier can comfortably carry. It also allows for best