I've never had any AR not function with any type of ammo I fed it. There are many factors that come into play with any issue of FTF,FTE,etc. to just start laying the blame on the ammo.
Most shooter's that complain about having problems with an AR don't know how to trouble shoot the weapon to know what is causing the problem,and most of the time,the shooter is the cause of the problem by not knowing the How-What-When's of owning / shooting / maintaining an AR15 in the first place.
Guy's buy or build a new AR,and they don't clean and lube it like it should be. Then they don't try to break everything in,sometimes things take a while to mate together to run like a fine tuned machine.
I don't know where some of you come up with these High powered - Low powered 223/5.56 ammo things. Factory ammo is loaded to SAAMI specs in the USA,and CIP specs in other nations.
The only low powered loads would be sub-sonic loads,and they are known to play havoc in gas guns.
Even if you hand load at a loading manuals starting load,it will cycle an AR with any bullet weight chosen.
Texas State Rifle Association
North American Hunting Club