The ideal weapon should be light enough to fit on a light truck, but powerful enough to outrange attack helicopters and armored scout vehicle.   A 40mm gun mounted on a simple pedestal would be ideal.   Scout-snipers rely on hearing and unobstructed views to pick out targets, so they should be not be enclosed in sophisticated turrets.  The gun may be manually aimed, or electric, and have a small magazine of less than 10 rounds to limit weight.  This is not a large, complex, expensive anti-aircraft system, just a Scout-Sniper with a 40mm gun.  It could be similar to the Bofors gun of World War II (left), but with some lightweight advances found in the modern one-ton Mauser 27mm automatic naval cannon (right).

 

       Hybrid electric engines can make motorized scout-snipers extremely deadly.  These engines normally run on diesel, but have large batteries which convert the energy lost through braking into electricity.  The diesel engines automatically shut off at slow speeds or while idle and the electric drive takes over.  This doubles overall fuel efficiently, and both engines kick in on steep grades or difficult terrain providing a tremendous boost in power.  However, the batteries can power a vehicle for up to 20 miles, so hybrid vehicles can revolutionize motorized scouting, especially at night.  They could switch to electric and move with zero infra-red and almost no audio signature, just the tires rolling along the ground.  

      The U.S. Army has successfully tested hybrid engines for its standard HMMWV light truck. (click for article)  A 40mm gun mounted on the bed of a hybrid HMMWV is perfect for a motorized scout-sniper.  The sniper would ride standing in the back looking for targets.  He would wear a thermal poncho to hide his own heat signature, as well as his loader, who also mans a machine gun for close-in defense.  

     The Bofors EL/70 (above) is modern and capable, but probably too heavy.  However, it could be simplified and streamlined to fit in the back of a light truck, more like the U.S. Navy MK-38 25mm gun (below).  However, the 25mm MK-38 is designed to fire like a machine gun, while the 40mm scout-sniper would require only semi-automatic and a few rounds.

      The sniper HMMWV would likely be paired with a hybrid-engine reconnaissance HMMWV packed with sophisticated detection equipment, including short-range radar, audio sensors, and FLIR.  These stealthy sniper-recon motorized teams would prowl the security perimeter of armored forces to provide immediate intelligence.  When they detect enemy reconnaissance vehicles and helicopters, the scout-sniper will take aim and wait for the best shot, then BOOM.  Even in open daylight engagements, the 40mm gun will outrange any attack helicopter or scout vehicle gun in the world today.  Attempts maneuver around the scout-sniper will only draw fire from other scout-snipers.   

        Even squadrons of attack helicopters would be forced to fight and destroy the deadly 40mm scout-snipers before attacking armored forces.   Scout-snipers may harass an enemy by sneaking up at night, placing a single round into a tent or vehicle, and then slipping away.  If an enemy employs high-flying UAVs, the snipers would practice some duck shooting.  Scout-snipers can play an important role in armored operations, they just need a bigger gun, a 40mm gun.