MKS Supply offers the answer to the mysterious cartridge groove.
Recently we received inquiries about Barnaul’s .308 Winchester and .30-06 hunting rounds. The .30-06 is an all American round once used by U.S. Forces as a military round but no longer. It is arguably one of the most popular and effective hunting rounds worldwide.
Note relief ring just above cartridge base.
The “mystery” is not really a mystery at all.