If you can find Soft Points or other controlled expansion projectiles (bonded hollow points, monolithics etc.) that would be significantly better than 55gr FMJ. You have AOA issues from 0-50 yards and velocity issues past 150 yards with 55gr and 62gr Green Tip. They are just not consistent loads for 5.56 in terms of wounding and without fragmentation or expansion, it's effectively a high velocity .22LR...
There's a reason that 5.56 has been so controversial among military troops over the last two decades. Some soldiers report it does it's job in 1-2 shots while others report having 5 to 7 consecutive through and through hits (ice picking) to stop an opponent at close range (not good, that's time wasted on engaging the target which NOT efficient and lots of ammo wasted that could have been saved for future use).
There's also a reason it's not legal to hunt deer or other medium sized game with 5.56 of any load in many states. Even with properly performing loads, it's wounding potential is not as good as intermediate or larger calibers. But that aside, if your going with a 5.56 upper in your arsenal (which I get due to commonality), load choice can give you over match against an opponent using 55gr or 62gr green tip.
Neither the Army (M855A1 monolithic copper slug with a steel penetrator tip) nor the Marines (MK318 barrier blind) use XM193 or M855 for anything but training purposes since around 2010. Yah they are better than nothing, but if you can find something else, I'd consider a better load. Your highest priority should be lethality, not quantity.
It only takes ONE encounter where you ammunition fails to perform for the bad guy to win. At that point it does NOT matter how much of anything you have. While that may be counter intuitive to the "prepper" mentality, that is the mentality that any higher tier unit takes, placing an emphasis on lethality (shot placement and load performance) vs. lower tier units. Combine that with higher levels of training and we have increased overall effectiveness.
While any load in any caliber can fail to incapacitate, some have very rare occurrences of failure (aka they almost always work) while others have frequent occurrences. I attached the 2008 Roberts report, but here are a few key points:
"The disturbing failure of 5.56 mm to consistently offer adequate incapacitation
has been known for nearly 15 years. Dr. Fackler’s seminal work at the
Letterman Army Institute of Research Wound Ballistic Laboratory during the
1980’s illuminated the yaw and fragmentation mechanism by which 5.56 mm
FMJ bullets create wounds in tissue. If 5.56 mm bullets fail to upset (yaw,
fragment, or deform) within tissue, the results are
relatively insignificant wounds, similar to those
produced by .22 LR--this is true for ALL
5.56 mm bullets, including military FMJ , OTM, and AP,
as well as JHP and JSP designs used in LE. This failure of 5.56 mm bullets to
upset can be caused by reduced impact velocities when hitting targets at
longer ranges, as well as by the decreased muzzle velocity when using short
barrel carbines. Failure to upset can also occur when bullets pass through
minimal tissue, such as a limb or the torso of a thin, small statured individual,
as the bullet may exit the body before it has a chance to upset. Finally, bullet
design and construction plays a major role in reliable bullet upset. Without
consistent bullet upset, wounding effects are decreased, rapid incapacitation
is unlikely, and enemy combatants may continue to pose a threat to friendly
forces and innocent civilians."
"5.56 mm BOTTOM LINE
Simply adopting new 5.56 mm barrier
blind combat loads that are optimized for
shorter barrels, offer consistent early
upset, along with adequate penetration,
and minimal AOA/Fleet yaw issues may
be the critical answer to many
deficiencies noted with currently issued
U.S. military 5.56 mm ammunition."
While clearly 6.8 SPC out performed 5.56 in all metrics of performance in that report and several others, 5.56 can be reasonably effective with the proper load design. Good luck!