It may be brass. I had some that were, several years ago. Try a magnet.
Dram Eq, and payload tell you nothing of the pressure the shell is loaded to.
You mentioned 'Old SxS' and that got me to wondering if you are assuming (wrongly) that these are low pressure shells.
They are loaded to SAAMI specs, which is all the manufacturer claims. They may or may not be suitable for the 'Old SxS'.
Do your homework first, and if your particular gun requires a lower pressure shell they are available from several sources.
Be safe.
