It hits the loading lever catch on the bottom of the barrel, when you pull it all the way forward.
He's talking about the cylinder axis pin that goes through the cylinder, about which the cylinder rotates.
Unless I'm mistaken.
Mine won't come out all the way, either.
On the 8" version, you can completely remove it because the loading lever catch is further forward.
Kind of like a Ruger Blackhawk 4-5/8". Axis pin won't go far enough to come out, without removing the ejector rod assy.
5.5", not a problem, as it comes out without removing the ejector rod assy.
Hope this helps.