Neck sizing for a wildcat

[Forester]

I am considering a 7-300wsm or 7-270WSM (same thing really) instead of a straight up 7WSM and have a few questions.

Is there any reason not to size 270WSM necks up (.007" change) instead of necking 300WSM brass down(.024" change)?

It seems like necking the 270 brass up would be simpler and should be doable in one step, If I use the 300WSM brass how many steps should I work through to size down that much?

I am planning or turning necks regardless so that is not a factor, I will inside ream them too if donuts look to be a problem.

 

[MontanaRifleman]

Hmmmm.. I would think to size up you would need to fire form and to size down all you need do is use a bushing die. Interested in hearing what the experts think.

Mark

 

[Forester]

6mmBR says size down from the 300WSM, but I don't really understand their reasoning.

At any rate, most seem to be doing it with the 300 brass and I am tired of sitting still on this project so I think that is the route I will go.

 

[MontanaRifleman]

The way I would go about would be to use the Redding Type S 300 WSM FL bushing die with expander button. Use a bushing that you estimate would leave you with right OD/ID after neck turnig for the tension you want using the expander ball to open it up enough to use your Reamer/neck cutter. Then turn the neckes then resize without the expander ball. Then trim after cases have been once fired. I found that my WSM cases actually shrunk a little with the first firing or two which require me to trim shorter after each firing.

 

[Mikecr]

If you're gonna turn anyway, Might as well size down about 5thou per bushing. But I would turn first(at 30cal), then size down, trial & error till it's right.
Keep in mind that down sizing increases thickness -fast.
You might also plan to leave a false shoulder to headspace off for fireforming.
This path will not produce doughnuts.

But some of this(strategy) depends on your chamber print to brass in-hand. I would look things over and understand a plan before proceeding one way or another.

 

[MontanaRifleman]

But I would turn first(at 30cal), then size down,

Just curious... why turn first, wouldn't you need to turn again after sizing down?

 

[Mikecr]

Turning mandrel fit.

When he sizes down the brass will gain 3-4thou in thickness and get wild.
Then he'd have to anneal and use every bushing and mandrel in the box trying to get a workable fit with his turning mandrel. Bad fit, bad turn.

On the other hand, It would be easy to turn a piece at 30cal, a few thou under desired, size down, & check thickness with a ball mic(or seat a bullet & measure neck OD).. Tweak the turn depth and do it again.
It's always trial and error with a turning setup. So I suggest he keeps it simple as possible, by fitting and turning the brass while it is in a normal state.

 

[MontanaRifleman]

Makes sense, thanks for the answer.

Mark

 

[Forester]

Turning mandrel fit.

When he sizes down the brass will gain 3-4thou in thickness and get wild.
Then he'd have to anneal and use every bushing and mandrel in the box trying to get a workable fit with his turning mandrel. Bad fit, bad turn.

On the other hand, It would be easy to turn a piece at 30cal, a few thou under desired, size down, & check thickness with a ball mic(or seat a bullet & measure neck OD).. Tweak the turn depth and do it again.
It's always trial and error with a turning setup. So I suggest he keeps it simple as possible, by fitting and turning the brass while it is in a normal state.

I can see the benefit of a quick clean up pass at 30 cal. to hopefully have the brass size down in a more uniform way. But doesn't the expander mandrel have more to do with getting a good fit to the turning mandrel than anything?

If I size down to bullet diameter, then use a sinclair expander to set the neck ID just larger than the turning mandrel then it should turn fine right?

After working the brass this much I was planning to anneal it anyway, should this be done before or after neck turning?

I ordered 150 pieces of Norma 300WSM brass, Dies and a small fortune in bushings so I should be getting started on this next week.

 

[Mikecr]

doesn't the expander mandrel have more to do with getting a good fit to the turning mandrel than anything?

Yes, I hope I haven't somehow contradicted this.

If I size down to bullet diameter, then use a sinclair expander to set the neck ID just larger than the turning mandrel then it should turn fine right?

Nobody loves the Sinclair system better than I. And it might work. But you should plan for what you need.
The 7WSM's neck is shorter than the 300WSM's by .054". Thats dangerous headspacing, so you'll need a false shoulder for fireforming.
This is good with the turning at 30cal plan. No need to turn up onto shoulders as .054" of the 30cal neck is going to end up shoulder anyway(eliminating any possibility of doughnuts).
And then you can just partial neck size for snug chambering.
You won't need to re-anneal Norma with a single direction sizing from 30cal to 28cal. Don't worry about it one way or another.

 

[Forester]

Yes, I hope I haven't somehow contradicted this.

Nobody loves the Sinclair system better than I. And it might work. But you should plan for what you need.
The 7WSM's neck is shorter than the 300WSM's by .054". Thats dangerous headspacing, so you'll need a false shoulder for fireforming.
This is good with the turning at 30cal plan. No need to turn up onto shoulders as .054" of the 30cal neck is going to end up shoulder anyway(eliminating any possibility of doughnuts).
And then you can just partial neck size for snug chambering.
You won't need to re-anneal Norma with a single direction sizing from 30cal to 28cal. Don't worry about it one way or another.

I am not fireforming 300wsm into 7WSM, I am building a 7-300WSM wildcat. In other words, a 300WSM, necked down to 7mm, no change in shoulder location. I won't have all that headspace because the reamer will be cut as though it were a 300, and the neck cut to something like .314 for the .284 bullet and .014 necks.