WRACo 6 mm USN with experimental primer

The previous thread on the .236 USN reminds me of a recent find in this caliber. It looks like a normal ball loading with a tinned copper jacketed 112 gr. bullet but it bears a ringed oval brass primer stamped with a “O” in the center.

WRACO Volume II p. 191 says: “Smokeless powder ledger indicates ‘Change lenght of primer cup 6 m/m and all similar. Cup (6 m/m) is now tinned & has no ring’ 9/22/98. (Author’s note: The mention of a ring in the first segment is a circle marking on the cup which was used to denote experimental. This does not refer to a ring crimp.)”.

An empty primed case using this primer and with a deep cannelure on the neck is also mentioned in “History of Modern U.S. Military Small Arms Ammunition, Volume I” p. 47.


This same primer can also be found loaded in .30 Army cartridges with headstamp W.R.A.Co. 30 U.S.G.


Is this primer similar to Winchester’s protected primer in having a sleeve around the cup? I ask the question because the quote “cup (6 m/m)” could refer either to caliber of the cartridge or, possibly, diameter of the primer. The Winchester 5-1/2 primer had a diameter of .236 in. Jack

Jack, this primer is a WRACo No. 2 1/2 W of .210" diameter (when crimped measures .193") and It is not protected. The ring diameter impression is wider than the typical W inside a circle.

Fede: Thanks for the response. The very heavy crimp and the bevel at the edge combine to render the proportions of this cartridge slightly difficult to grasp. Jack