Need someone who has reloaded for some time and understands why case dementions come out as they do, to give some info as why this is happening. I have used mostly Norma cases for my 7.7 Jap and have worked a load that is accruate at 100 yards. (Average .375 groups) I reformed some 30/06 cases to the 7.7 which is done a lot with the 7.7. I used the same dies and settings and then shot a few rounds with them using the same primers , bullets and powder loads. I noticed on the fired 30/06 reformed cases that there was an area .354 distance from the head on the case that seemed to a slightly brighter then the rest of the case. So I took some measurments of 4 fired Norma cases at the head and then .354 from the head. They came out:
Head Diameter- .480, .479, .479, .472. And then .354 from the head-.480, .477,.472,.479.
Then I measured 4 reformed cases:
Head diameter- On all 4 was .469
.354 from the head was-.480, .481, .480, .481.
on all the reformed 30/06 cases the head was, on the average, .011 smaller than the Norma cases after shooting. A Remington factory case before fireing or reforming was .466 on both measurments. What is happing here with the reformed case?

Forgot to say the reformed rounds did not shoot as good a group either. (.375)

I'll get this right in a minute. The groups with reformed cases went from .375 to .500

The 30/06 case is undersized in the Jap chamber.
I have never use Norma cases but they probably are the right size.
Good Luck!

Thanks Hawkins. Probaly best to stay with the Norma cases. Just wondered why this was happening.

It is amazing on this forum that when you are really looking for good answers no body answers. But say something about a certian brand rifle,etc and experts(?) fall out of the wood work!

Why is this happening?

If you chave a case that fits the chamber perfectly and your round has no runout, then the bullet points straight down the bore and flies true.

If you have an undersized case in your chamber, the bullet will point away from the bore centerline. It will enter the bore crooked and won't fly true.

Hence, the difference in accuracy

Sounds right on the undersized case causing a difference in accuracy. Found out a lot of people are reforming 7.7 from 30/07 cases and shooting them even though they come out undersized. After I fired a few and seen what was happining I quit using them.

Ackley warns of this exact combo...


in order to use 30-06 brass, and have it FIT, the barrel must be set back and rechambered for the 06 brass...

measure some norma's, right at the web (just above the cut) and see what that reads... .002 is fine... but the 06 starts life as .473 at the largest... iirc the jap is .482

jeffe

quote:

Originally posted by Blob1:
It is amazing on this forum that when you are really looking for good answers no body answers. But say something about a certian brand rifle,etc and experts(?) fall out of the wood work!

Really?

If you are getting .5" groups with reformed 06 cases especially with a 7.7 just keep using them.If you don't go nutsy Fagen with the pressure and stay away from head separation you'll be way ahead of the game. I did years ago and if I had a 7.7 with the accuracy you're getting I'd do it again.Enjoy roger