a solution to avoid collapsing shoulders especially when necking up (7SS to 338SS)

[MAD10]

If you aren't familiar with Sherman Wildcats. Rich sells his 338SS brass with a 7mm neck and you are required to neck up. The amount of shoulders I was randomly collapsing was alarming. I was following known practices such as using a three step process to achieve the .054 of neck expansion required. Specifically carbide mandrels in .30 cal, 8mm and 338. I chamfered and deburred the brass and lightly lubed both the mandrel and inside the case neck. I should note my failures were at the 8mm step and on the first attempt each time.

I spoke with Rich Sherman after I had expanded all my necks with the .30 cal mandrel without issue. He suggested I try my 338SS FL sizing die and keep the sizing button on the stem to open the necks to 338. Well **** it worked perfectly!

I treated the brass just like I was FL sizing a piece of fired brass, with one exception, I did not run the brass fully into the die I only went just enough to feel the neck run over the button. I will say it is wise to check the sizing button after you've sized a few necks to be sure it's not threading off the stem. Also runout was 2-3 thou.

NOTE: The mandrels were Sinclair carbide expanding mandrels. IMO it seemed the short travel was too abrupt without the case being supported as it was in a the FL die. Verse much longer mandrels, such as 21st Century mandrels, which are longer and have a more gradual taper. The 8mm mandrel taper was .250 to .322 in a very short distance so that may have something to do with it. However, I had no issue with the 30 cal mandrel of similar taper and length.

Disclaimer: Using a FL sizing die to expand necks might be a common solution but it wasn't for me. I only used "like" caliber mandrel diameters for neck tension and removing dents - to see shoulders collapsing was co$tly.


Sincerely,

 

[LRNut]

Did you try lubing the necks? I have to do this sometimes even when not expanding necks.

 

[can1010]

your right the Sinclair aren't the best option, if you have a lee universal decapping die use the lee expanders in that they have a long taper also use powdered graphite inside the necks it makes a big difference

 

[Marky_mark]

Did you try lubing the necks? I have to do this sometimes even when not expanding necks.

I do this now with my 338 ss brass and have no issues sizing them up

 

[HandgunHTR]

I used to do the "neck up in steps", but after years of wasting time with my TCU cartridges, I now just do it all in one pass with a tapered expander in my FL die. .22 to 7mm in one shot.

Don't spare the lube on the inside of the neck either. It is much easier to remove lube than it is to deal with collapsed shoulders.

 

[MAD10]

I do this now with my 338 ss brass and have no issues sizing them up

Thank you … yes I'm using lube I cover that in the second paragraph

I wrote too much trying to make sure I didn't waste people's time having them respond with solutions.

I failed in my goal of pointing out "using a FL sizing die with the 338 button works very well to expand these necks"

I should have just stated my solution vs the issue I solved and I apologize to all for not being more concise.

 

[Revolting Peasant]

Thank you … yes I'm using lube I cover that in the second paragraph

I wrote too much trying to make sure I didn't waste people's time having them respond with solutions.

I failed in my goal of pointing out "using a FL sizing die with the 338 button works very well to expand these necks"

I should have just stated my solution vs the issue I solved and I apologize to all for not being more concise.

Nope. Your first write up was perfect, had all the info I needed plus the background info. Sometimes knowing what didn't work is just as valuable. Rock on!

 

[akmtnhnt]

I've found graphite lube specifically to also be key.