The M1128 Stryker Mobile Gun System has made its mark. You can see why in this video, where a slight hiccup with the main gun is overcome, and the gun goes off. However, does it truly match up with the M551 Sheridan light tank?
The Shillelagh had a range of 3,000 meters. It didn't work that well, and is only combat experience was being used against bunkers during Operation Desert Storm. A Sheridan could carry nine Shillelaghs and twenty "normal" rounds for the M81 gun.
The Sheridan did see a lot of combat in Vietnam, where it was both loved and hated. Its gun was very good at providing fire support, but it had a much slower rate of fire than the M48 Patton. Still, the Army bought over 1,600 Sheridans. The Sheridan was also the only armored vehicle that could be dropped in with the 82nd Airborne.
Now, let's look at the M1128 Stryker Mobile Gun System. Like the rest of the Stryker family, it is an eight-by-eight wheeled vehicle. It fired the same M68 gun used on the M60 Patton and early versions of the M1 Abrams tank. It holds 18 rounds.
The gun is also mounted on an external weapons station with an autoloader. The M1128 can't be air-dropped, though, but it can be flown in on a C-130.
Both vehicles have a .50-caliber machine gun and a 7.62mm machine gun to handle infantry threats. Neither are capable of resisting anything more powerful than a 14.5mm machine gun, although the Stryker can take additional armor (at the cost of mobility).
Both gave the Army's lighter forces some extra firepower. But the Sheridan had some clear advantages over the Stryker, while the Stryker offers some improvements over the Sheridan.
Really, though, the best of both worlds was probably the XM8 Armored Gun System. This was a light tank that had a XM35 105mm gun, and could hold 30 rounds for its main gun (plus the .50-caliber and 7.62mm machine guns). The system was also able to take add-on armor to protect it against a number of battlefield threats. Sadly, it was cancelled in 1997.