Conrad,
Great to hear everything worked out! On a side note, I do not know the size of the magazine end cap screw off the top of my head. I'd suggest taking it to your local hardware store where they have those screw sizing templates and checking it for diameter and thread size. Also from your PM, I have not had a loading problem like that. Could there be a burr on the inside of the mag tube end? The mag tube housing on the barrel is tapered to allow shells to make the transition but there could be a small lip if the tube is off center for some reason. Have you checked to see that it is not the shell stop in some way blocking the loading of the shell? With the rocker shell stop used in this era there is adjustment that can be made in the forward set screw at the front of the receiver on the right hand side.