Okay, how much can you take off the outside of the neck before it becomes critical. Just mic'ed some 300 win mag Norma cases that were neck turned and there is .014" to .016" neck thickness. When I neck turned them, I rotated them to 4 different positions around the mandrel and there was some brass taken off 98% of the neck. If I just locked it down once and neck turned then only 50 to 60% of the neck was shaved. Concentricity improved when I rotated and neck turned. This was in a Lyman manual trimmer so it's possible the mandrel was not perfectly aligned.

Also measured some new never fired Nosler 30-06 cases and they were from .012" to .014", very consistant. These new cases are already thinner than the turned 300 win mag cases.

My question is can I turn some more off the 300 win mag cases and try to get perfect neck thickness?

bench rest shooters run wall thickness as thin as .0085" But this is in guns with tight neck chambers where the brass can not expand. For my factory gun, i make one cut of the brass getting a full cut the first time. Wall thickness is never less then .012" (243win rem & win brass)I have not had any necks split after 10 firings, loading with bushing dies. Follow the Lyman instructions, full length resize using a standard die and expander button before turning. Make sure you give the fl die at extra 1/8 turn after the shell holder hits the die bottom so you can get a cut clean to the shoulder of the case.

Woods, if you are turning necks and are still running.002 difference in the extreams of thickness, you are no better off than when you started. As far as perfect neck thickness is conserned, I have not been able to do that either but I can come a heck of a lot closer that factory brass. I turn for a .330 neck in all the 30 cal that I shoot and come within .0002 on the vast majority of them. I have never seen any of the lathe type turners that did a better job than what you are doing now, and use a couple of different turners now leaving them set up to the thickness that I want, simply go from one trimmer to the next without having to adjust any of them. Other than being a bitch to adjust, I have found the Sinclair trimmers are as good as any and better than most in the quality of the cut.

Woods:
There are two reasons to turn case necks.
1. to fit a cartridge to a tight chamber.
2. to improve case concentricity.
In the former you have a targeted case neck thickness. This is determined by subtracting the "release" you want from the actual chamber's neck dimention. Subtract the bullet diameter from this number. Divide the result in half. That is your desired neck thickness.
The latter is a self selected case wall thickness. My procedure is to set up my cutter so that it peels about 80% of the average case neck surface area. This is a trial and error setup and very subjective. It is important to remember that you don't want to over thin the case necks. The cases would have worked fine without ANY material removal, so some caution is advisable.
It is also good to remember that for a "factory" chamber thinning the necks means you will be working this brass more, there by reducing it's usefull life.

muck

quote:

Originally posted by muck:

It is also good to remember that for a "factory" chamber thinning the necks means you will be working this brass more, there by reducing it's usefull life.

muck

True. Plus, with new unfired brass OR fully resized brass, it will also mean that the loaded round, before it is fired, will be slightly LESS centered in the chamber. The loaded round lies in the bottom of the chamber before firing, and the thinner neck diameter overall will leave the cartridge neck/ & bullet less well centered. That can be corrected by having the bullet touching the lands prior to firing, but that approach is not highly practical in hunting rounds. (Too much danger of having a bullet stick in the bore if extracting an unfired round becomes necessary.)

quote:

Originally posted by muck:

It is also good to remember that for a "factory" chamber thinning the necks means you will be working this brass more, there by reducing it's usefull life.

muck

True, and it may require the use of a bushing die, as the neck may have become too thin to be sized down enough for proper bullet tension in a standard die. FWIW, Dutch.