If both wounds wewre entrance wounds and neither bullet left the body, what sort of round/caliber, ammuition would have been used? Even a 22 is likely to have come out from the hit to the throat.

A pistol bullet, for example, entering the middle of the throat could lodge in the cervical vertebrae and not exit the body. Or the bullet may have first gone through the front windshield of the limo (as has been theorized), reducing its velocity before entering JFK's throat. Remember that the .38 bullet shot from Ruby's gun at point blank range was still in Oswald's body. So if the bullets were fired from lower velocity weapons, and/or fired from long range, and/or first went through another object, they could have certainly remained in JFK's body. And yes, a smaller caliber round such as a .22 would be more likely to remain within the body.