The 40 gr has good speed, flat trajectory and can be devastating.
When stretching it in tough imperfect conditions I have found it to come up short.
Stepping up to 50 gr gets better specs for density and bc.
A 52 gr hollow point is also popular and loaded by many makers Blue Box, Red Box and Ultramax
Byron South did a write up and chose to step up to 60 gr BT in his AR.
Over the years many of us have seen splashes, spinners and runners. Some get up after a period of time.
The .223 just doesnt have the authority of the next larger calibers, so imperfect shots show.