We're all familiar with the weapons the GIs carried during World War II, but a gun just ain't much use without the ammo. The GIs, as Star Trek's Scotty once famously admonished, needed the right bullets for the right job.
The ammo that the GIs used ranged from the famous .45 ACP to powerful artillery rounds. In a training film, released in 1943 and linked below, the Army took the time to show what the more common rounds could do.
For most WWII-era artillery, the effective range was quite short. Anti-tank guns, for instance, were rarely impactful against targets more than a thousand yards away. Today, anti-tank missiles, like the BGM-71 tube-launched, optically-tracked, wire-guided missile, reach out about two and a half miles or more. The bazooka, potent at 200 yards, has its modern counterpart in the FGM-148 Javelin, which kills tanks over 2,000 yards away.
It's also interesting to note that the ammo and weapons are quite versatile. The Browning BAR, primarily known as an automatic rifle intended to send hot lead downrange at enemy troops, was also an effective option against enemy aircraft. The 37mm and 57mm anti-tank guns weren't exclusively useful against enemy tanks, but also against pillboxes and other fortifications. The M2 .50-caliber machine gun was devastating against aircraft and troops alike.
In a sense, today's ammunition is just as versatile. For example, the AGM-114 Hellfire was originally intended to kill tanks, but has also been used turn high-ranking terrorists into "good" terrorists.