The bullet exiting his chest at Z270 per your sketch , how could it not have gone thru his hat held in his right hand if there was an exit wound at the base of the palm?
The brim of the hat is gripped by his fingers. Whatever may have exited on the volar side of the forearm/wrist
located 2 cm above the wrist crease was some distance from the hat brim.
Could you draw another sketch with how you think he’s holding the hat with the right hand?
This is how he held his hat:

If the official wrist wound description is correct that the entrance found was top of hand at the wrist and the exit was at the base of the palm then…
The hat had to be held in the right hand upside down so that the upper side of the right hand is hit first and the exit at the base of the palm follows.
The entrance wound was 5 cm or 2 inches above the wrist crease on the back of the forearm. The hole in the french cuff was an inch above the end of the cuff:

The exit wound on the volar side was 2 cm or .8 of an inch above the wrist crease and was a small transverse slit ie. in the same direction as the crease.
There was a slit in the shirt sleeve just above the french cuff:

but it was not a transverse slit and its position does not correspond to the slit in the skin on the volar side of the wrist.
That is a bit odd if the slit in the shirt was caused by something exiting the wrist. If the entrance on the back was an inch above the end of the cuff and the slit in the skin was 1.2 inches lower toward the end of the cuff, whatever caused that transverse slit on the volar side should have missed the end of the cuff by .2 inches or .5 cm.
So in your sketch for the angle of the shot at Z270, it looks like a hat in the right hand held upside down between both legs would have a bullet ( or fragment ) exiting the palm go thru the well of the hat.
You should not make any assumptions about the object that caused the skin break on the volar side. It could have been a bullet fragment or a bone fragment. There were 5 bone fragments found in the wrist. I am not sure it wasn’t possible that a sharp edge of a bone fragment in the wrist penetrated the skin during the 5 minute trip to Parkland as JBC rolled around in the car. The slit in the shirt had to have been caused by something other than an exiting object because it is over 2 inches from the slit in the skin and it is at a right angle to it.
If one draws a line from the exit point on the wrist it looks to me that if something did exit the wrist it would have missed the hat brim and well of the hat.