Proper neck wall thickness?

[Savage99]

I made 308's from 30-06 and liked it. I found a bunch of military brass in the reload room and decided to try this, now I want to make other cartridge brass from the military stuff (so I don't have different ID's on the head stamp).
Anyway, here is my question; What should the neck wall thickness be? I have not seen a source for this measurement. I am going to be purchasing a Lyman outside neck trimmer shortly and the book "Cartridge Conversions.....".
Here is what I have done so far:
Cartridges of the World, 11th edition, chapter 20 (Cartridge ID by Measurements), the number under "rim thickness" didn't make sense so I took bullet diameter and subtracted this from "rim diameter" and divided by 2 and came up with a number that made sense.
SAAMI diagrams-did the same math and came up with different numbers from Cartridges....(didn't make a table, just random notes)
This table is from the SAAMI diagrams
308 .3435-.3090=.0345/2=.01725 parent (mil)
30-06 .3397-.3090=.0307/2=.01535 parent (mil)
25-06 .2900-.2575=.0326/2=.0163 parent (mil)
22-250 .2540-.2245=.0295/2=.0147 to be made
243 .2760-.2430=.0330/2=.0165 to be made
250Sav .2856-.2580=.0276/2=.0138 to be made
300Sav .3390-.3090=.0300/2=.0150 to be made
I am using a case gauge and calipers (the very tip)
So what should the neck wall thickness be? I want to be as accurate as possible and I know I can only go out 3 decimal points.
I am an Engineering Technician and question things when the numbers don't match up.

[country gent]

Depending on how involved you want to get and your chambers actual dimensions neck wall thickness can be what you need. Brass cases do vary from maker to maker and lot to lot. Loaded round dia is whats important here. A round to big wont release the bullet freely and evenly increasing pressure and other issues. A chamber cast of the chamber will give you the neck dia of the chamber. A fired case can show this also. A quick check is to try and put a bullet into the fired case if it drops in you are ussually okay if tight or snug there is an issue. Neck wall thickness can vary with the cartridge also. SOme like 44-40 38-40 are very thin others are thicker. Normally you will find in range of .008 -.012 thickness on a side. Benchresters use a tight necked chamber where the neck dia is known and the Loaded round dia is turned to be .0005-.001 under it to maintain concentricity between chamber and round. With reformed cases sized down necks thicken allowing for this type of fitting woth a factory chamber. Forming 243 win from 308 brass is an example, its is normally to big a neck to chamber freely as formed and needs .001-.003 removed from dia to be free so fitted rounds can be made.

[EDG]

See the SAAMI and CIP standards for case wall thickness.
We can all have opinions but those two organizations are the real and final authority on civilian brass and ammo.
If you want military data you can search the Assist Quick Search site.

http://www.saami.org/specifications_and_information/index.cfm

http://www.cip-bobp.org/homologation/en/tdcc_public

If you are not familiar with reading these drawings let me know. I can help you.

Cartridges of the World is nearly worthless for this kind of data since it is of unknown origin - it is certainly not a reference fot the industry. It is just a hobby book. It will get you in the ball park but it is not recognized by any industry as an authority for manufacturing ammo.

You can calculate your own thickness if your brass is only going to be fired in one rifle.
Measure the NECK ID. Measure the bullet.

Subtract the bullet from the neck ID. Then subtract .006 and divide by 2. This gives you .003 clearance on a side. I like them a little tighter for best accuracy but .003 should keep the newbies out of trouble.

[Savage99]

thanks gents. I am going to use the SAAMI specs for what I am doing, as these are in units that I am used to working with. EDG you are right about the Cartridges of the world for dimensions, I have found it to be just a hobby info source and something to read. I am doing these conversions as an exercise. I did some looking around and did measurements on factory brass and they are all different depending on the cartridge. I previously thought this dimension was all the same. I learn something new everyday and all the time. Thanks again