I have a Smith and Wesson M&P AR-15, and was wondering if any one out there had found that perfect load for it.
So far I've just been using the max load of Win. 248 with 60 gr Nosler balistic tip or Hornady VMAX.

...or maybe someone has a AR 15 that has a 1 in 9 twist and a 16" barrel that fires 5.56?

don't matter what my rifles like your's won't.
i have three 223's
one likes aa-2230 and the spsx bullet
one likes the old aa-2494br powder and the sierra 52 gr match bullet.
and the last one likes the hornady 53gr match bullet best with h-4895.
the armalite gets aa-2230 and 55 gr fmj's
it hit's coke cans at 100 just fine and will ring the 300 yd 12" gong as long as i care to shoot at them.
yours may like any or none of the above.
in a semi functionality takes precedence,then ultimate accuracy.
if they happen to coincide cool, if not reliability is king.

None digest the same loads exactly even consecutive serial numbered Rifles , it's a trial an error equation .

If it were only that easy ! One of mine loves Bulk or name brand 55 grain or Sierra Hornady 69 ,68 grain with BLC-2 24.5-25.5 makes lovely dime sized groups eats nearly anything respectively .

My other one is a little more finicky but favors 75-77 grain with 21.5 of either H335 H322 an makes bolt shooters cry with 2-300 meter groups. Both are Bushmasters E2S 20" target units with chrome lined bores and whom ever it was who said chrome bores weren't target quality if FULL OF BS !!!.

My 1 in 9 twist Armalite loves these two loads with 60 grain Hornady V-Maxes: 25.5 grains of Win 748, and 23.3 grains of the new IMR 8208 XBR powder. Commercial brass and CCI 400 primers.