Preferred Neck Wall Thickness

T

TScull

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I'm having a reamer made for a new barrel and can therefore choose my preferred neck wall thickness and chamber clearance. The cartridge is a 7 mm short magnum. After researching the clearance issue, I have settled on 0.003 inch diametral clearance. I have not however gotten a handle yet on the issues associated with neck wall thickness. I have read about walls of about 0.0085 inch used for 6 PPC. Some go as high as 0.0160 for some larger calibers. I know I will have plenty of starting wall thickness since I will be necking down 300 WSM cases.

Should I leave them as thick as possible, removing just enough to clean them up? Are there advantages to getting them to some minimal thickness such as for round-to-round bullet grip force consistency? Should there be a relationship between caliber and wall thickness?
 
From my experience

It would be better to leave them as thick as possible and there has been some activity lately with folks using "No Turn" cases for new chamberings. The thinner one gets a neck the more fragile it becomes and the more likely to seperate from the shoulder. I think the thinner necks harkens back to the day when brass wasn't as good as it is now.
 
Here is what I do.

Make a case first. Set up a neck turner and see what the cases will clean up 100 percent to with a minimum amount of removal. Then, have you reamer ground to fit that neck.

When I dveloped my 30PPC, I did just that. I made the cases, found out that a .332 neck would be perfect, then had Dave Kiff grind my reamer accordingly.

With brass such as Lapua, all you are talking about is a few thousanths to turn at the most. But with some brass that has a larger wall thickness variation, you might have to count on taking a little more off to get them to clean all theway.......jackie
 
On a hunting gun such as that why not go with the saami chamber and shoot it. What are you realistically going to gain in a WSM by turning the necks?
 
It's not for hunting.

The gun is intended solely for long distance (600 to 1000yard) tactical target shooting. The action is a Sako M995 repeater out of a TRG-S rifle with a 30 in, 1-in-9 in Krieger barrel. Accuracy with a high ballistic coeficient bullet (Berger 180 gr VLD with a claimed BC of 0.684) at a reasonable velocity (2850 to 3000 ft/sec) is the goal.
 
I would get 100 pieces of Norma 300 WSM brass and do exactly what Jackie suggested. I would also have my Redding dies and a Kiff headspace gage before I determined the headspace that I wanted on the finished barreled action.
It sounds lke a fun project.
 
Response to Jay's comments

Jay,

Dave Kiff will be making the reamer for me. I just sent him the drawing but have not finalized all the dimensions. This neck wall thickness question is intended to help me decide that dimension.

I was planning on having my gunsmith, John King of Kila Montana, use the chamber reamer to make up a Wilson type case holder for use in my trimmer. I'm figuring this could also be used in conjunction with calipers as a headspace gauge.

I'm planning on having Niel Jones make the full length resizing die for me, with a couple of different neck bushings. Neal makes his dies from cases fired three times in the finished chamber.

After reading all I could on brass manufacture, I'm leaning toward using Winchester. My plan is to turn the necks, uniform the primer pocket, ream the flash hole, weight sort and probably anneal. After doing all that, I assumed there is no benefit to spending twice as much for Norma brass. I have read that Lapua brass lasts a long time but they do not make the WSM cases. Could I expect longer life from the Norma cases or are there other benefits I'm missing?
 
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Skull

It has always been recognized that Norma Brass is a cut above in adhereing to tight manufacturing tolerances. Their brass tends to stand tall in minimum wall thickness variation and overall quality of the case dimensions than most domestic brass. Lapua is a cut above all, but as you noted, they do not offer WSM brass.

Winchester is quite good, though. With careful case prep and sorting, you probably will be quite satisfyed.......jackie
 
Since you're already turning I'd take another thou off the N. D. Incase you swap brands later and they turn out thinner. I would say take more but an autoloader may dent the necks on ejection.
 
Norma and Winchester 300 WSM brass are different size at the base. Also 7mm WSM and 300 WSM have a different headspace. Make sure you have a reamer that you have to turn the neck. Don
Oh by the way I still sell neckturners.
 
Norma versus Winchester base size

Don,

I didn't realize the base would be different for the different brass. I'm glad you told me. I'll make sure I buy my brass and measure it prior to finalizing my reamer dimensions.

By the way Don, do you have a web site? I was interested in looking at your turner but couldn't find where they are sold.

Tim
 
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