Sizing @ shoulder diameter

[memilanuk]

So... I've got a bunch - maybe too many - .308 Winchester dies. Dang things are like rabbits, I swear

Recently I was comparing some of the sized dimensions of cases coming out of some of the various dies. Some of them, like neck size and shoulder bump, the user has some degree of control over in how they set up the die in the press. Others, like sizing at the 0.200" line (case web), less so. Another that seems to fall into that latter group would be the sized case diameter at the shoulder. Today, I'm solely interested / asking about this last one: shoulder diameter.

For the sake of argument, assume 'premium' brass, 2x fired in a custom barrel / custom action. Fired diameter just below the shoulder/body junction is ~0.455", +/- 0.0005" on my Mitutoyo digital calipers. Also for the sake of discussion, I'm going to forego the inclusion of all the extra half thous here and there, as they're technically outside the true capability of the tool (to my understanding).

Brand 'M' sizes the shoulder to 0.453"
Brand 'R' sizes the shoulder to 0.453", but another brand 'R' die (same model/line, but a 'small base' version) squeezes the shoulder down to 0.450"
Brand 'F' sizes the shoulder to 0.453"
Brand 'W' sizes the shoulder to 0.455" ie basically not at all

I've got a few more hiding somewhere around here, but these are the ones of interest at the moment.

Looking at the numbers, it answers one question - why I was getting such unusual case growth when using the brand 'R' SB die. It also raises another question: should I be concerned about the apparent lack of sizing at the shoulder from brand 'W'?

What would you expect for a 'normal' amount of sizing at the shoulder diameter, just below the shoulder/body junction? All else being equal, any concerns about *minimal* sizing at that point?

 

[dgeesaman]

$0.02

Tony Boyer looked for .001 sizing of the body near the shoulder on 6PPC fired from single shot actions. Custom chamber, custom dies.

It takes a few shots to fully form the brass to get a good “chamber sized” brass.

For a single shot rifle I’d get close to Tony’s number. The less the brass sizing, the less it will pull and stretch the brass. Less trimming, longer brass life, etc.

More sizing than that is probably necessary for a repeater and certainly for an AR-10. My factory dies have always sized .003-.006 on diameter at the shoulder. Of course that functions in every imaginable case, but 99% of the time it’s extreme. When I want a cartridge to perform it’s very best I buy a custom die to get .001-.002 sizing.

 

[Chaotik]

I don't usually check my shoulder diameter on sized cases, and perhaps I should. I wonder if that area is not sized to a certain minimum, can it cause a stiff/hard bolt lift?

 

[quest450]

my BRA 3x fired brass is .4610" and .4600" sized with a custom die

 

[Doom]

As for the W die the specified maximumcartridge dimension is 0.454" to 0.446" so it slightly exceeds the SAAMI specification but the minimum chamber dimension is .4551" to .4553" so you are basically at the limit but should be OK.

I would expect most dies would size around 0.453".

 

[Straightshooter1]

So... I've got a bunch - maybe too many - .308 Winchester dies. Dang things are like rabbits, I swear

Recently I was comparing some of the sized dimensions of cases coming out of some of the various dies. Some of them, like neck size and shoulder bump, the user has some degree of control over in how they set up the die in the press. Others, like sizing at the 0.200" line (case web), less so. Another that seems to fall into that latter group would be the sized case diameter at the shoulder. Today, I'm solely interested / asking about this last one: shoulder diameter.

For the sake of argument, assume 'premium' brass, 2x fired in a custom barrel / custom action. Fired diameter just below the shoulder/body junction is ~0.455", +/- 0.0005" on my Mitutoyo digital calipers. Also for the sake of discussion, I'm going to forego the inclusion of all the extra half thous here and there, as they're technically outside the true capability of the tool (to my understanding).

Brand 'M' sizes the shoulder to 0.453"
Brand 'R' sizes the shoulder to 0.453", but another brand 'R' die (same model/line, but a 'small base' version) squeezes the shoulder down to 0.450"
Brand 'F' sizes the shoulder to 0.453"
Brand 'W' sizes the shoulder to 0.455" ie basically not at all

I've got a few more hiding somewhere around here, but these are the ones of interest at the moment.

Looking at the numbers, it answers one question - why I was getting such unusual case growth when using the brand 'R' SB die. It also raises another question: should I be concerned about the apparent lack of sizing at the shoulder from brand 'W'?

What would you expect for a 'normal' amount of sizing at the shoulder diameter, just below the shoulder/body junction? All else being equal, any concerns about *minimal* sizing at that point?

My virgin .308 Lapua and Alpha brass measures .451" and Peterson's is .452". After firing, they all measure .455". I use a Forster FL sizing die that sizes them all down to a consistent .452" (very little springback as I anneal my cases after every firing).

If brand "W" chambers smoothly, there's shouldn't be any concern, though any dirt and crud that might enter there could be an issue while out stomping around hunting.