i did not forget about the stopper rings.
I have a idea or 2, but usually I would use tig wire here for stopper rings as tig wire bends very easy.
on the stopper ring I would use 2,4mm tig welding rods.
depending on size, I would clamp the tig welding rod tip onto a 14mkm steel round bar.
from there I would turn it by hand.
then when all is done I would cut trough all the rings with the small angle grinder, fit swivels and then silver solder them closed.
I like a big stopper ring.
but 12mm steel round bar will work as that is double the slide inside diameter.
you will never pull a slide over a stopper ring