Take a 5-6" long piece of very stiff 1/16th" D wire like a piece of Piano wire (model airplane hobby shops have it) then take a file and shape a single bevel point on to one end of the wire. Next bend that shaped end to a 90 degree angle resulting in a little tit about 1/4" long with the bevel to the inside of the bend.
No bevel on this one but it gives you the idea
Now stick this inside a used case and using it like a probe feel along the inside of the case just ahead of the base. If there is a stretch ring you will feel an indentation in the wall of the case just ahead of the base.
ON a case like a 30-06 after firing and resizing about 3-4 times this slight dentation will start to appear. by 5-6 firings it will be very obvious and an indication the brass should no longer be reloaded.
On straight wall pistol cases like .45ACP this stretching never really takes place and some short fat pistol cases can be reloaded as many as 25 times.