7.7 Arisaka

[Visionz45]

Ive began loading for my 7.7x58 Arisaka using .30-06 lake city brass. The brass was annealed prior to being run through my resizing die and come out to 7.7 without issue. I understand that .30-06 case head dimensions are smaller than 7.7x58. Ive fire two work up charges, 43.0gr and 43.5gr of IMR 4064 behind a 182 gr .3105 hungarian heavy ball projectile. My primer have back out(slightly) on both. My case neck expansion is .007 and I see no "char" marks around the primer, no stick bolt lift either. The primers after being punch out are in two pieces, anvil and cup. Before I go any further, the thoughts of metal part intermingling with human parts nags me pretty bad, so, Low pressure (under pressure) or high pressure..any thought?

 

[Visionz45]

P.S. its an early war, 1942 Kokura series 23 with a chrome bore and good rifling.

 

[Kernel]

You say you worked up those loads. If so, what did the primers look like at, say, 41 and 42 grains of 4064?

 

[Sport45]

You may have excessive head space. Try backing out the sizing die a full turn and then running your .30-06 brass though it. Check it in the rifle's chamber. Run the die in 1/8 turn at a time until the bolt takes the slightest effort to close. That should take care of your primer backing out. If those cases get shorter with successive firings it's an indication of not having enough pressure to stretch the case back to the bolt face after the firing pin and primer have pushed it into the front of the chamber.

My Arisaka really likes the Hornady 174gr bullets that are .312 diameter.

 

[Steve Marshall]

Low pressure and/or excessive headspace. Sport45 gave you good advice.

 

[Visionz45]

Sport45 was right on the money. I followed his directions and the problem has been remedied. Now what would be too tight? Ive set mine so that it requires a good push of the finger to close the bolt. Accuracy has improved from 4.5" to around 1 1/4" to 1 1/2".

 

[Sport45]

If you can close the bolt with one finger I'd say that's not too tight.

 

[Visionz45]

Thanks, I'm always a fan of double checking with half century old rifles.