The WC bullets tests were meant to show what happens to a Carcano bullet at full-speed and striking hard tissue (bone) nose-on. The result was mushroomed and deformed bullets, quite unlike the CE399 "pristine" bullet.
This was supposed to demonstrate that CE399 didn't strike bone at full-speed nose-on but rather was a bullet consistent with having been slowed passing through soft-tissue (Kennedy's neck), no longer nose-on when glancing along Connally's thin fifth rib (further slowing and more off-axis) to arrive at the radius no longer at full-speed nor nose-on. Thus no mushrooming or major deformity of the bullet.
The Warren Commission probably figured the public was sensible enough to understand and appreciate such tests. Instead, the critics saw an opportunity and claimed the test bullets showed what CE399 should have looked like.
There was a 2004 program called "Beyond the Magic Bullet" that did a more direct replication of CE399, using torso-sized casts and firing a Carcano rifle from a distance and height comparable to the SN in Dealey Plaza. The crane holding the "sniper's nest" was swaying in the wind. Thus the shot arrived a little low into "Kennedy" than they hoped. The "Kennedy" torso had no simulated bones so passing low and exiting the chest on the model was just more soft tissue compared to the real Kennedy's neck. The "Connally" torso did have "bones" that the test bullet struck. They found the bullet on the ground and it was in one piece with a squeezed appearance, similar to CE399.
The SBT shot in 1963 was one-in-a-million. If the gunman had waited a second or aimed a micro-degree different, it would have been a different set of wounds being discussed. Replicating it means the odds are heavily stacked against it. The 2004 test came close.