These are made from WW2 era 30.06 cases. Case length is 2.250. Caliber is .308, 150 grains, soft point. From base to shoulder they measure approx. 1.875. Cartridge in middle is a 30.06 shown for comparison.
About the only dimensionally similar round I see in my list of .30 wildcats is something called the .300 ICL Tornado. Of course, it could be someone’s one-off wildcatting project.
They might be 7.7 m/m Arisaka. Before Norma-made ammunition became available in the mid-1950s people did resize .30-06 brass for this caliber and, .311 bullets being in short supply, used .308 diameter for the job. The .30-06 brass is a bit small at the base to be ideal, but it was done–not, be it understood, that I’m advocating the practice. Jack
7.7 x 58 Jap
It wasn’t unusual to run a .30-'06 chambering reamer into the 7.7 chamber, then shoot .30-'06 in them without further ado. Apparently it worked OK. Roy Dunlap in “Ordnance Went Up Front” described how tons of captured Type 99 7.7 rifles were given this treatment after WWII for use by the Koreans or maybe the Nationalist Chinese, I don’t remember which. I’ve seen one sporting rifle made up from Japanese Type 99s this way also.
A trick sometimes used when the case head is slightly smaller than the chamber diameter is to run a thin strip of masking tape around the base so it centers the case in the chamber. When fired, the case then expands to fit the chamber uniformly instead of bulging on one side. I did this first when converting .30-'06 brass to 7.7 many years ago, and have also done it in making up 6.5X55mm cases from .30-'06 or .270 cases, and .303 Savage from .30-30 brass without incident. However, I use only milder loads.
It was South Korea that used 7.7 Arisaka rifles rechambered to .30-06. I am not saying that China never did this also, but I would tend to doubt it, since China also made 7.7 Japanese ammunition after the war, as well as 6.5 Arisaka. They used plenty of Japanese weapons, of course, in China, as well as weapons from about every other major country.
Undersized cartridge bases can be a real issue. Unlike a neck split, which is seldom of any consequence, a split through the base of a cartridge is pretty serious stuff, especially if it goes on through the head as well. Probably what saves the day here is that the Type 38 and Type 99 Arisaka actions are among the strongest rifle actions ever made.
The great weakness of the .30-06 rechamber of the Japanese type 99 rifle is that the chamber is advanced forward about a quarter inch (6.5 m/m) in the shoulder area, greatly reducing the thickness of the barrel at this point. This is because the barrel is a relatively light one, and the barrel contour closely follows the chamber shape at the rear. What was in the original caliber a reasonable margin of safety in terms of barrel thickness is seriously reduced here. I know of one case in which a stateside rechamber (7.7 to .30) resulted in a ruptured barrel and a serious injury to the shooter. The first publication mentioning the original U.S.-sponsored conversion of these rifles for the South Korean government of which I’m aware was M.D. Waite’s interesting article “Japanese rifles and carbines” in the February 1958 issue of the American Rifleman. Jack