MILES58 - Last night I worked on my old Win M12.
First I got the correct screwdriver for the job. smile
Took the magazine tube apart without difficulty.
It did have a dowel for a plug. Everything looked
okay and I put it back together. As it turns out,
that was not the problem.

So ... it must be the shell stop.
Looking into the bottom of the receiver I can see
the shell stop. It is marked '16' and it is clearly
jammed. It maybe also worn or broken.
The shell stop is the problem.

Next question --
How do I remove the shell stop ?

Thanks for your help.

"Far better it is to dare mighty things, to win glorious triumphs, even though checkered by failure, than to take rank with those poor spirits who neither enjoy much nor suffer much" Teddy Roosevelt