need stevens model 11b advice

[damn yankee guns]

I'm an old guy starting a new career in smithing. I admit I am still lacking in some figure it out skills.
I have a stevens model 11 pump that after shooting will slip a shell in under the shell stop and jamb the gun. I have replaced all the small springs and tuned the slide release spring. I've replaced the slide stop and the rifle still releases the shell early. The chamber seems a bit sloppy and the shell moves around a lot in the magazine at the shell stop. What is my next option. I need some gunsmithing help. To all the friends and experts out their, thank you very much. I hope I can help all you fellows out sometime.