I have a particular 338 WM, new this year, producing some once-fired cases that hold 87.8 to 88 grains of water. (measured without primers, using masking tape on primer pocket).
The 338 WM is typically rated at 86 grains of water and some new WW cases hold 85-85.6.
Also, the area immediately in front of the belt of the once fired cases mics at .5156-.5164" after firing, which is big in my opinion.
Current 'new' WW cases mic .508, while the SAAMI spec at that point is .513.

So is a chamber that produces once-fired cases with 87.8--88 grains water capacity, and .516" diameter on the body shaft at the belt, too large?

Should I consider sending it back to its factory/importer, or just load for it as a 'wildcat', with a slightly larger capacity than 338WM?

Fortunately, the chamber is fairly concentric and the once-fired cases give variance like .5156-.5163 or .5157-.5164 for a case. Rifle seems accurate, sub-MOA capable, though we're still in the load development stage and yet to reach 100 rounds.

It's easy enough to limit this gun to neck-sizing and special loads that may use 2-3 of grains of powder more than expected or than my other 338s.

In confirmation of the above, most of the loads with various bullet weights chronograph about 100 fps slower than expected and slower than other 338s I own. This would seem to support the idea that the chamber is a bit larger than typical.

So any advice, opinion?

If you neck size you should try one of Lee's collet neck sizer in 338WM. They are great. I think you can only get it in a set with a seater($28) but it is worth the price for the sizer if you throw the seater away. I had a Weatherby Vanguard in 338 WM and I only NS for it for 10yrs. At the time I used a Redding NK sizer with the stem and bell taken out and the necks opened to .336 with a Lyman 338 M die. If I had to it over i would get the lee die.

quote:

The 338 WM is typically rated at 86 grains of water and some new WW cases hold 85-85.6.

"Typically rated" is not a SAAMI spec, you're okay.

Fat Albert

Thanks, and I already enjoy the Lee NeckSizer. It is great.


Jim C.

Yes, water is not a SAAMi calculation, but brass diameter is, and .516 at a spot rated for .513 is where I'm having questions about the acceptability of the rifle's standards, to accept it, or to request a fix.

What you are seeing is pretty standard for a factory chamber - they come in all sorts of sizes! In particular, chambers for belted magnums are sometimes cut on the ample side.

I would not worry about the extra couple of .001" here and there. Except, if you "luck" into a FL sizing die on the small side, you may be forced to trim cases with every FL sizing.

A couple of things you can do:

- as mentioned above, neck size. At least until your cases become too stiff to chamber, and then you are forced to FL size.
- I personally prefer to PFLS, setting up your FL die to ensure your cases headspace on the shoulder. Much smoother chambering, and brass life will be good.
- If you still find you have to trim after every PFLS, then have a die made to match your chamber. Hornady will do it for you from a couple of fired cases, cost is around 120$, or so.

- mike

Without taking a cast of your chamber you can't really tell if it is oversized or out of specs.

I think you are over thinking the situation. You are not getting ruptured cases so why not use the Partial Full Length resizing method (that I prefer) and see how many reloads you get from a case? If you get half a dozen or 10, your chamber is fine.

IMO, a 100fps difference between rifles of the same make and calibre is a nothing. And I certainly wouldn't red-line my powder charge trying to make them match.

Doing a partial full lenght size is the last thing you would want to do. If the cases are oversize at the base, when the case goes into the fl die it will push in on the sides of the case and that will push the shoulder forward. I had this problem with a 280rem win 70 that I bought for a real good price(found out why). Even with the FL die touching the shell holder it made the fired cases were too long. At this point it was eather NK size or trim off the bottom of the FL die so the fl die could push the shoulder back down and this overworks the cases. I went with NK size and never had to FL sizes the cases.

quote:

Yes, water is not a SAAMi calculation, but brass diameter is, and .516 at a spot rated for .513 is where I'm having questions about the acceptability of the rifle's standards, to accept it, or to request a fix.

What you're missing is the difference between SAAMI max specs for the cartridge vs. the chamber and, perhaps, how those specifications are written.

Loading book drawings only show the max cartridge dimensions and those specs have a tolerance range, it's not a specific point. Chamber specs also have a tolerance range and the minimums are always larger than the maximum cartridge specs. It's done that way to insure that the largest ammo will work in the smallest chamber of any rifle ever chambered for that case. Factory ammo is typically a little smaller in all dimensions than the smallest SAAMI ammo spec. so we can't measure it to establish anything except that's what it is for that round. Part of what handloading offers us is the opportunity to deal with those small differences in a more precise way.

Fired case dimensions are typically about 1 thou smaller than the actual chamber dimensions. A difference of 3 thou forward of the belt is within the normal range of the respective spec differences. Your chamber isn't oversized and you need not adjust your charges other than to follow the rule of "Start low and only move up to book max unless you see high pressure signs earlier."