Well you are describing exactly what the 223 crowd denies. They are claiming it functions like any other hunting bullet. That is closer to being true than stories about 5.56 bullets doing damage by wild bullet path. It is true that a light bullet at HV will change path easier than a slower, heavier bullet. But the wild wounds are not the norm. There was a wives tale in RVn that AK ammo was designed to tumble because of a void between core and jacket. That was wives tale too. I’ve shot several hundred groundhogs with GI 5.56 and if you didn’t hit them in the head or spine they would head for hole. It had about same effect as running them through with a ice pick. The speed did cause a suction that if you gut shot an animal it would run off trailing intestines. I shoot 55gr bullets in 222, 223 & 220. The old GI 55gr was 3250fps, I don’t know what grain they are using now but it’s heavier. That means it’s going slower and is going to deflect less.
Are you shooting them with a nonexpanding 55gr FMJ? If so I’m not surprised at all that terminal performance was dismal.