How much neck tension ?

[shawnba67]

I am going to try and modify a cheap set of 30-06 AI dies for my new 8 mm06AI. My loaded rounds measure .345-346. How much smaller than .346 should it be for a hunting rifle type use? I realize this is cast boolits but since it matters it will be J words at least for now.

[TheDoctor]

I was always taught and read that for j-words, .001 under bullet diameter, and more than that was not any more effective, and leads to more run-out. Seems I like the word "more" today for some reason....

[RickinTN]

For quite some time I have attempted on jacketed-bullet hunting/accuracy loads that somewhere between .001" to .002" works pretty well. I do like enough tension with hunting loads to keep the bullets put during transport. I have had bullets seat themselves deeper because of vibrations in an old truck and on an airplane. Because of this I purposely chose a bullet with a cannelure to load for a friends' fly-in bear hunt and crimped which I seldom do. I have tried with my cast bullet endeavors to keep the neck tension about .001" and I've had pretty good luck. I have loaded cast with as little as .0005" tension and they felt as though only the "sticky" of the lube was holding them in place and the loads shot well.
Good luck,
Rick

[BK7saum]

I try for 0.001-0.002" neck tension on j-words. Some of my case ammo is 0.000" and crimped. Yep, my m-die expander and sized boolits are the same size or my expander is a few ten-thousandths smaller. I find that there is enough spring back that the they don't seat deeper or move under recoil. Of course these are for revolvers. If a semi auto. I would go with 0.001" minimum and a good taper crimp.

Brad

[shawnba67]

Thanks guys. I hope I don't screw this up. Doubt I'll find more Ackley
dies cheap lol

[Artful]

You might check how much it sizes down your brass
- lots of dies I have size down way more than required then when pulling back over the expander ball
it pumps then up closer to what is required
- if you measure before sizing then run it into the sizer dies without the decapping pin
and measure it, it will show how much it really swages the neck down.

You adjust by just changing out the decapping pin's expander ball.

By the way make sure you smooth up that ball as by being rough it also
affects the amount the case is worked and can even stretch your brass.

[country gent]

I too would set it up for .001-.002 tension. Leave it a little small so the expander ball has .001 to expand back up. To much for the expander and holding shoulder length and angle gets harder as the ball may pull it up also. To little and neck wall thickness variences become an issue

[EDG]

This is the diameter of the neck ID for 3 8X57 dies that I have measured.





8X57



RCBS

FL

.3430


8X57


LEE

FL

.3410


8X57


PACIFIC

FL

.3400

[Doc Highwall]

I would recommend .001"- .002" my self which is what I like about the Redding bushing dies in that I only have to change the bushing.

[John Boy]

Even though this is a CAST BOOLITS forum Shawn, the rule of thumb is:
Jacket bullets = land diameter to 0.001 over
Lead bullets = 0.001 to 0.003 over groove diameter

[shawnba67]

This is the diameter of the neck ID for 3 8X57 dies that I have measured.





8X57



RCBS
FL
.3430


8X57


LEE
FL
.3410


8X57


PACIFIC
FL
.3400



Thank you very much, that information is tremendously helpful

[country gent]

When working this dimension up the way figure the rough starting point is. Neck wall thickness X2 + bullet dia- interference wanted= neck dia so a .323 dia bullet +.010 + .010= .343- .002= .341 for .oo2 press fit with brass that has a .010 thhick neck