I saw the movie again. Other than the SABOT rounds being used on the gunships, there was nothing conventional about the handheld guns that held the SABOT rounds, at least to typical viewer. They those guns from Sector 7. It's possible that the guns used modified SABOT rounds, ones with a chemical propellant. It certainly would have been in the interest of Sector 7 to develop a weapon that could harm the alien robots.

 

I was also thinking that, if this were a Marvel movie and Sector 7 was S.H.I.E.L.D., I would expect them to have some sort of advanced weaponary.

Sabot:- a casing surrounding the projectile that breaks appart when a round leaves a barrel, a scalpel blade with break apart casing loaded into a Pistol is now a Sabot.