Maybe the smell of old deteriorated powder?
OK, I opened many different cartridges, some much older that M1 Carbine, and never had any smell of vinegar. I admit that I have not intentionally stuck my nose inside of them too. And on the same day? What does this mean? Smell it in the morning and later the same day?
Good powder should have the smell of ether or an acetone smell but the bullet must be pulled so the smell of the cartridge would be tied to the case.
I recently observed and smelled some deteriorating caseless cartridges. Upon opening the drawer they were in, there was a distinct acetic acid/vinegar smell, but after some time passed the smell went away. Perhaps the “same day” reference means you should smell the powder the same day you pull the projectile? Just a wild guess.
Not Vinegar as such, but an Acrid, Nose-burning Acid smell (it is actually Nitric Acid one is smelling) although the Nitric acid is much stronger (in pH terms of activity, the effect on the nasal membranes is the same as strong vinegar…).
Caused by the breakdown of Nitro-Cellulose by absorption of water, which returned the Powder to its original “Cellulose Hydrate” state, and releases Nitric Acid (HNO3) to attack the inside of he case (especially if steel).
Problem usually found in WW II German steel cased ammo (43-45) due to short-cuts in Powder Production (incomplete dryiong out of the Powder, and incomplete washing of the Nitro-cell7ulose to extract the excess Nitric and Sulfuric acids used to Nitrate and dry the Mass.
Normal Canister Powder over several years old will also deteriorate in a similar manner, and the tin cans will rust from the inside out…,.and may combust spontaneously.