You should really pay more attention to what's said and happening in NV. The Securitron's did not have pistols, they had submachine guns attached to their arms. And if you speak with the NCR commander outside of Primm, he tells you plainly, that the NCR is stretched too thin to supply him with extra troops, thus not allowing him to retake Primm, unless the Courier can convince the commander at Mojave Outpost to allocate some troops. A lot of NCR commanders tell you this throughout the wasteland, that they can't properly defend what territory they do own, because their forces are ill trained and spread too thin to react to any intrusion by legionaries crossing the Colorado river, or other factions who aren't friends to the NCR. Also, the NCR has no contact with the citizens of Primm, they're all hiding in a casino, so how they would coordinate anything is beyond me.