How can you make such a statement when you don't know what the combined weight is of the fragments that are still in Connally's body?
Aren't you forgetting those fragments recovered from Connally during surgery that Audrey Bell gave to either an FBI agent or a Secret Service agent?
Dr. Gregory estimated the largest fragment deposited in the wrist to be five-tenths of a millimeter in diameter to approximately two millimeters in diameter. In looking at the X-Ray of the thigh, said that the fragment in it was about 5 tenths of a millimeter by 2 millimeters. At those dimensions, the lead fragment would weigh 17.8 milligrams. One grain is equivalent to 64.8 milligrams. So, those two fragments together weighed about 1/2 of a grain.
A postoperative X-Ray shows a tiny fragment left in the wrist. Gregory referred to it as a needle in a hay stack. It was so tiny that it wasn't worth the effort to try and remove it. Combine that fragment with the three small ones removed from the wrist and you'd really have to stretch the imagination to get their total mass up to 1/4 of a grain.
Here are the fragments removed from Connally by Dr. Gregory:
Audrey Bell gave them to Texas Highway Patrolman Bobby M. Nolan. Bell recalled that he wasn't in uniform. He probably wasn't, which was not uncommon for Texas Patrolmen back then.