I am having a very strange problem with my 20ga AL 48 Hunter. When I load the magazine full the gun will shoot everything but the last shell that in the mag tube. The last shell doesnt load into the chamber it remains in the tube. If I load it back up with one in the chamber it shoots fine but doesnt feed the last shell.

I have strip it down and cleaned the entire gun but the problem still exists. I checked the mag spring and it seems to be fine. Has anyone else had this problem with theirs? Any ideas on how to fix it or trouble shoot it? Thanks in advance for any ideas of help.