I've read a lot in the FAQ secion and many other sources on ammo for AR15's.

Still, I can't seem to decide if I can use 5.56 in my weapon or not.have
The lower has Match Target Competition HBAR II Cal .223

Ser # CJC02xxxx

I've used Wal-Mart Winchester white box .223 ammo exclusively and fired around 2,000 rounds with this rifle with never any problems.  

End of this month is the local gun show - can I safely use any of the surplus military ammo?
I don't want the Russian made stuff, but I see Q3131 and M193 offered.  

Any suggestions would be greatly appreciated.hn,

oh man get all the xm193 you can i like the lake city, but the winchester q3131a is just as good. oh and yes your  gun can shoot the miltary m193 and the m855 green tip. both are loaded hotter than the commercial stuff you get at walmart. happy shooting!!!

As long as your barrel is marked 5.56 NATO you can shoot both. Dont worry about the lower markings.