...not what Guinyard claimed to see.
In reviewing the "split case" issue on several gun forums, it does appear that splitting occurs when the chamber is too large for the shell, as was apparently the situation with Oswald's revolver. One guy specifically mentioned an inability to eject the shells. However, he indicated a single split case prevented the ejector rod from working at all. So, we would have to picture Oswald, on the run, opening the cylinder, attempting to use the ejector rod, realizing it didn't work, and shaking the shells into his hand or prying them out with his fingers. All of which sounds a bit unlikely on the run, seconds after the murder. Unless the gun wasn't fully loaded when he shot Tippit, he would still have had two live rounds and it's difficult to picture why he would have been desperate to fiddle with the gun.
Trying to picture what Oswald actually did, and why, is one of my favorite sleep-inducing exercises. Sort of like counting sheep.