neck clearance

[whiskey08]

I have a chamber with a .338 neck. My loaded rounds measure .339. How much clearance is recommended between loaded cartridge and chamber? Would a loaded round at .336 work? (.300 wsm)

 

[artbosco]

I have a chamber with a .338 neck. My loaded rounds measure .339. How much clearance is recommended between loaded cartridge and chamber? Would a loaded round at .336 work? (.300 wsm)

The 30BR performs marvelously with .002'' total clearance [.330" neck chamber with a loaded round measuring .328" on the neck at the pressure ring.] No reason to believe that your 300WSM wouldn't work well with the same clearance .338" minus .336" = .002". You might also want to try .335" for an additional .001" [.003" total].

Word of caution: Ensure the neck chamber actually measures what you think it does.

 

[Laurie]

Wiskey08,

you don't say what your .300WSM is being used for. 0.002" (total) clearance, or a mere 0.001" at any particular point around the case neck circumference is an absolute minimum safe figure, and in a benchrest rifle at that. Any fouling or dirt can cause major problems with a less than whisker thin clearance of that nature. Also, how are your neck-turning skills and what measuring kit in the way of a tubing or case-neck micrometer do you have? You're into measuring and turning things to tenths of a thou' at this level, and the turning needs to be really consistent around each and every case's neck. If you need a lot of ammo, hence lot of brass, that's a great deal of case preparation work, as each neck has to be coarse turned, then finished turned to get the desired results.

Even many 6PPC benchrest shooters are moving towards 0.003" total clearance these days.

Moreover, there is a growing feeling that too tight clearances can reduce accuracy with larger cartridges, many reckoning on 0.003" minimum or even a bit more for 6.5-284 for instance. I don't know what the .300WSM precision shooters reckon is best, but I'd be surprised if it's as small as 0.002". I'd go for (total) 0.003" clearance minimum and a fair bit more if it's a sporting rifle.

 

[whiskey08]

thks guys, the rifle is a long range hunter. I will shoot a couple of long range tactical comps with it, just to get used to the rifle. Either way im sure ill be rolling around in the dirt. .003 of clearance does sound more practical.

Right now my brass measures .0155. To get down to .335 from .339 that means ill have to take off .002. Do you guys see any issues with the remaining neck thickness of .0135

this will be the first time turning necks, im sure ill go thru a handfull of cases trying to figure it out, but i dont spending the time to learn a new skill.

 

[RonAKA]

If you are working with tight clearances, then also be aware that a neck can have a taper in it. Suspect it may have something to do with cutting a clean neck with the reamer. But, if you are comparing the cartridge neck diameter to the chamber diameter, it will matter where on the neck you measure, if there is a taper.

 

[Steve Blair]

I use .004 for 7mm and .30 calibers in F-Class.

 

[tenring]

A tip: Most case wall thickness mics have a flat end on the spindle. This makes it difficult to measure some necks; in paticular very short necks, like the .223 or Dasher. I had the end of my Mitutoyo spindle turned down by my smith so that the flat end is only about .030" wide. It works well

 

[Catfish]

With my tight necked chambered gun I trun for .002 neck clearance. On my 224 TTH and my 6-284`s I get a ring in the back of the neck which causes excess presure so I have to inside neck ream them from time to time. After a couple of times my necks get get thinner so I go to a .002 smaller bushing which gives me .004 expantion and brass life is great. One thing, you need a bushing .001 smaller than you want the OD of the brass as it will spring back .001.