If you could buy them in the US ( don´t know if some dealers sell tem) try this sort of ammo.
It is swiss army standard ammo ( Gewehrpatrone 90)   and a special load for the SIG 550 assault rifle. It has a 63grs FMJBT bullet and produces 960 meters per second and best of all : it´s highly accurate out of 1/9 barrels. I´m able to fire 19 mm groups at 100 meters ( Versa-Pod on the ground 10 shot , wind slightly right 3km/h) . The groups open up to 42mm at 250 and in the best case 61 at 350 meters. I don´t know what you get, but this is the most accurate 5,56x45 factory load at payable price I ever fired. They cost here 300Euro per 1000 rounds and thats cheap in comparison to Hirthenberger ( 1Euro per shot ) and PMC 55grs ( 0.69 Euro per shot ; 1 Euro = 1.18$)

They were (or still are?) available from ammoman for a while, and everybody pretty much agreed that it is one accurate round. As a target round it was superb, but not so good as a defensive round, as it is made intentionally NOT to fragment.

But from the target shooting point of view, the stuff, if still available, makes for one heck of a good buy.