both have proven very capable. the 5.56/223 has proven it's lethality to a few thousand humans the hard way and 45ACP has done so to millions.
the 45ACP is a heavier bullet(up to 5 times the mass of the standard 223) traveling much slower however those heavy slow movers hit like a Mike Tyson right hook. all that weight has a price however, the effective range for something like deer, even from a carbine is barely over 100 yards.
the 223 however is very light and very fast. it hits, disintegrates and keeps going. a lot of times it's penetration through flesh is it's best feature and saving grace. it's effective range for deer is well into 200 yards and coyote hunters regularly use the 223 at ranges past 300 yards.
EDIT: Vmax explosive wound patterns is a very good analogy. Vmax is designed for varmints; small animals that require very little penetration to reach the vital organs. Vmax pretty much disintegrate on contact and pretty much shreds the soft tissue, light bone and thin hide dropping varmints in their tracks however for larger animals this does nothing mroe than give them a horrible flesh wound with tiny bullet fragments that have little hope of anything making it past a should bone or ribs.
all guns lost in a tragic smelting accident.
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