Were these sons of Nippon armed with 6.5s or 7.7s

10 years ago 2 years ago

Bore Size in Jap Military Rifle

by Nick Harvey 10 years ago2 years ago

Q: I intend reloading for a 7.7mm Jap rifle for use in military rifle competition. One reference lists the bore diameter as .303″; groove diameter .315″; groove depth .006″. I question these figures. Can you tell me what the proper bore and groove dimensions as well as groove depth is for the Japanese Model 99 Arisaka rifle in 7.7x58mm rifle? What diameter bullet gives the best accuracy in these rifles?

Bob Wilson

A: It is possible that some Jap rifle barrels may have those dimensions, but I have found that groove diameter is more likely to be near .312″. Reloading Manuals recommend use of .311″ to .312″ diameter bullets. A friend of mine who is a keen gunsmith- experimenter tells me he has found that .308″ bullets will give the finest accuracy in the 7.7mm Jap rifle. Use of a larger diameter bullet may well result in unnecessarily high pressures.

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Posted by Nick Harvey

The late Nick Harvey (1931-2024) was one of the world's most experienced and knowledgeable gun writers, a true legend of the business. He wrote about firearms and hunting for about 70 years, published many books and uncounted articles, and travelled the world to hunt and shoot. His reloading manuals are highly sought after, and his knowledge of the subject was unmatched. He was Sporting Shooter's Technical Editor for almost 50 years. His work lives on here as part of his legacy to us all.