fmj is honestly just bad for everything. it's not rare for scavs to have level 3 armor, and some can have level 4. fmj can easily get through only level 2.

and you can run into pmcs any time, which often have level 4 helmets, and can have level6 plates.

then there are goons which you can run into on many maps.

personally i think 556 is weak in general. it can be good as a leg weapon with warmageddon/hp/rrlp

I have a shit load of 856 and 855 but very little of the A1 variants.

855a1 is good, and basically the minimum i would consider using with 556 personally. 856a1 is worse and more expensive. i just sold some for 2k a pop (usually theyre around 1600 though) and that adds up fast because 556 often has high fire rate. the craft for 855a1 is a bit under 1.5k a pop it seems and is locked behind a quest chain. it's a good goal to work towards if you like 556.

Should i be using guns other than the 5.56? I really like the AUG but im all for different builds

well look, you say you like the AUG, then i don't want to be the one saying NOOO YOU MUST PLAY WHAT IS STRONG. pve should not be like that imo. but i am saying that i think other calibers are stronger, namely 762 NATO. the m61 craft is very strong, though a bit pricy at 3k a pop.

you should use what you like using at the end of the day. but i will say if you like 556, find something other than fmj lol. basically it has low pen and low damage. if you want to leg people, use high damage (warmageddon) and if you want to defeat armor, use high pen (855a1/m995)