Psssht. I sneer upon your paintball sentrygun.
You know what the army is building?
"The Advanced Tactical Laser, Boeing's Flying Laser Cannon"
THATS A FUCKING DEATH RAY.
Also, railguns;
Railguns work by electrically generated magnetic repulsion, no toxic chemicals or propellants involved--so yay, finally a gun that kills people and not the environment! In the test pictured above, the projectile was fired with an electric charge of 10.6 megajoules, that's a one second pulse of 10.6 million watts, or enough electricity to power the average American household for a year. When applied in a single split second to an aluminum slug that's much, much smaller than your house, it's enough to make the slug do Mach 7. For those of you who just imagined a seven blade razor, first pretend you're not an idiot, and then try to conceive of something moving fast enough to ignite the air around it and to fuck up anything it strikes in ways science barely understands.
And finally:
Modular Disc-Wing Urban Cruise Munitions (i.e. Exploding Flying Saucers)
Thats basically the manhacks in Half Life 2 only they explode. EXPLODE.
Soldiers of the future are fucked.