.338 Sherman Short Mag build

[elkaholic]

The ss line but not the Sherman (long action)

 

[ruby76]

How much did you have to shorten the Hornady die? I'm going to start messing around prepping brass, have some RP 300 saum to practice on. I seen you posted pushing the shoulder back .084, have any other specific measurements (neck length, oal, neck wall thickness etc).

 

[El Matavenados]

I was aiming to shorten the die by 0.100". As for other measurements, Elkaholic has a write-up in a thread. Do a search for "6.5 SS (Sherman Shortmag)" thread under the rifles, bullets, barrels,etc forum, and look on page 6.

He also provided the following for the 338 SS:
"Neck wall should be turned to about .014 at 7mm because it will thin when you neck it up. You should shoot for around .0125" at .338 or around .362 to .363 neck o d with bullet loaded."

I'm starting with 300 SAUM brass, so I'll have to fiddle with those numbers a bit.

 

[ruby76]

I was aiming to shorten the die by 0.100". As for other measurements, Elkaholic has a write-up in a thread. Do a search for "6.5 SS (Sherman Shortmag)" thread under the rifles, bullets, barrels,etc forum, and look on page 6.

He also provided the following for the 338 SS:
"Neck wall should be turned to about .014 at 7mm because it will thin when you neck it up. You should shoot for around .0125" at .338 or around .362 to .363 neck o d with bullet loaded."

I'm starting with 300 SAUM brass, so I'll have to fiddle with those numbers a bit.

Perfect, thanks. All the searching I've done and I hadn't seen that post.

 

[elkaholic]

I would trim to 1.945" at fire form length because it will shrink .010 to .015" when you form and your chamber is 1.940". Also, this will take a little trail and error unless you wait until you are necked up to .338 before you trim. I would leave the shoulder bump a little short and you can bump a little more with the ss die if necessary. YOU CANT BRING IT BACK IF YOU GO TOO FAR! Turn the neck to .0125-.013" at .338 diameter. Your chamber neck dimension is .368". I would turn the neck back to about 1.605" from the case head. If you try to get things too close before you have a chamber to check headspace in, and no dies, you MAY waste some brass.....rich

 

[El Matavenados]

I created this shell holder for my mill, so that I could use the mill to inside ream the case necks. When I planned it, it was thinking I might also buy an outside neck turning tool that could be chucked into the mill. This unit was also capable of accepting the K&M carbide neck turning pilot with donut cutter. Together, those tools would cost about $150, so I'm going a different route. I'll still ream the inside of the necks in the mill. This fixture will also allow me to do the final trim to length after fireforming, which would otherwise require a custom case holder from LE Wilson. But with as straight as the casewalls will be, the Wilson cutting system might not even work.

 

[elkaholic]

Let me know how that works out. We have found that sometimes "too rigid" can cause angled reaming if everything isn't perfectly in line. Sometimes allowing the reamer to "find center" can be the best option.

 

[El Matavenados]

Let me know how that works out. We have found that sometimes "too rigid" can cause angled reaming if everything isn't perfectly in line. Sometimes allowing the reamer to "find center" can be the best option.

I think you are right. I chucked the reamer up into the mill, and noticed a lot of run-out. After running some tests, it looks like there is at least .0015" run-out in the spindle, and the reamer is pretty long, making it very obvious. If holding it lightly in my fingers doesn't produce acceptable results, I'll have to go a different route.

The fixture should work well for trimming, though.

 

[El Matavenados]

I reamed the cases with a .307 reamer (I'm starting with 300 SAUM brass). This left the neck walls at .015" thick. I outside turned one down to .014", then ran it over the mandrel in the .338 SS die. This brought the neck walls thickness to .0135 (measured with calipers). I have a tube wall micrometer coming, which will allow me a little more precision. But I'm estimating that turning the necks down to .0135 before sizing to .338 should put me very close to the goal.

 

[Pdvdh]

Sounds like you could manufacture the casings from solid brass tubing. Not convinced all your efforts are necessary, let alone beneficial. But it sounded like the goal was to reduce cost, so maybe it saves money.
The more time spent playing with wildcat cartridges and custom rifles, the more certain I am you'll conclude it costs money. And you'll likely reach the conclusion that it's money well spent.
This coming from a confessed miserly member...

 

[elkaholic]

I reamed the cases with a .307 reamer (I'm starting with 300 SAUM brass). This left the neck walls at .015" thick. I outside turned one down to .014", then ran it over the mandrel in the .338 SS die. This brought the neck walls thickness to .0135 (measured with calipers). I have a tube wall micrometer coming, which will allow me a little more precision. But I'm estimating that turning the necks down to .0135 before sizing to .338 should put me very close to the goal.

I talked to JGS and the reamer should ship 2/20

 

[El Matavenados]

I talked to JGS and the reamer should ship 2/20

Cool, thanks!

 

[Farmerbrown32]

Any news on the 338 ss? Looks like a very interesting cartridge.

 

[elkaholic]

Any news on the 338 ss? Looks like a very interesting cartridge.

One is chambered and will be in the owners hands soon. The reamer is at another smith, and 2 more waiting. Should be data this month.