ok just an observation on my part but I would rank them in sales this way. top seller 223....semis use lots of ammo then 30-30 30.06 .270 308 .243 7mag 7.08 300 win mag.....all the rest. This is just for Pa....other areas may be different.

One thing for sure, the .308 is not going anywhere, and 7mm bullets are more popular than ever. So, the 7mm-08 is pretty safe as it is easy to make from .308. I can't really think of any older cartridges that you can't get or make brass for, ie. .257R, 7x57, 30/06, 250 Savage, .218 Bee, .221 Fireball, .220 Swift, 22 Hornet, 22K Hornet, 25/20, 32/20, 45Colt, 44/40 and the list goes on and on.