and giving it's troops Service Rifles?

The only way those are going to kill most any type of creatures (including Legionnaires) in the Mojave is by giving it lead poisoning long after its killed the trooper that shot it.

I suppose that maybe the rifle and ammo is just cheap to manufacture, or they found a pre-war storehouse full of them, which is debatable considering when the AR-15 was first developed and why (NATO).

I guess "one shot, one kill" concept is obsolete, even in the wasteland, except for maybe Rangers... I also find it a little strange that the average Legionnaire recruit and prime seems to have better firearms (hunting rifles, cowboy repeaters, 10mm smg's) than a NCR trooper... and rock their [censored] up close too with a machete to the face.

also how is it that the NCR drove the Brotherhood out of Helios one? a .223 or 5.56 doesn't even get through power armors DT? not that the BoS have it any better... Laser Rifles pack about as much punch as a high powered flashlight.

anyways, its not a plot hole per-say, but it doesn't seem that well thought out to me.