Neck turning Alpha brass in 6mm GT

[neckturner]

So moving to 6mm GT from 308 is turning out to be an adventure all unto its own.

For context, I've turned a lot of brass, mostly Lapua 223 and 308, and mostly just skimming to remove high spots, but also a lot of tight-chambered 6mm PPC. This Alpha 6mm GT brass has presented a new challenge, and before I accost the Alpha people, perhaps the collective wisdom of this forum can help.

The new challenge is tapered neck thickness. The necks start at .013" or less near the mouth and thickens to .014 or a bit more near the shoulder/neck junction. I'm reluctant to turn it all down to .013, because that means a finished OD of .269 and the SAAMI spec is .273, which in theory works the brass a fair bit with each firing - but I'm not an expert on how much free play in the neck is too much. On the other hand, turning it to max .014 - just skimming near the shoulder - makes it .013 near the mouth and .014 near the shoulder, so a .001 taper in the neck tension, which can't be a good thing.

Pics below.

Thoughts? Should I turn it to .013? Should I complain to Alpha and get new brass (given that I'm in Canada and this could take weeks or months or longer)? For all I know a tapered neck isn't terribly out of the ordinary, but I think it is.

Thanks in advance!

Sequence showing neck thickness - notice it goes from just over .012 to a solid .014:

Results of turning to about .0138":

 

[Ccrider]

I would go with the .0138 and never look back. Maybe not quite as much into the shoulder.

Load a bullet with the turned piece and measure to see what your loaded round actually is. .003-.004 works fine. You will not be able to shoot the difference if there is one.

 

[NiteQwill]

Is there a reason for neck turning Alpha 6 GT brass?

I literally have thousands of Alpha 6 GT OCD and non-OCD brass, adopting it in its infancy... Heck, I have unopened boxes I have won at matches still sitting unmolested.

I have shot many, many barrels out for 6 GT. My process has simply been clean, anneal, FL size with 265 bushing, trim/chamfer, load. It is such an easy caliber to load for that going from 0.2 to 0.1 groups, due to neck turning, is simply not measurable in shooting ability. And IMHO, not worth the effort.

 

[neckturner]

I would go with the .0138 and never look back. Maybe not quite as much into the shoulder.

Thanks - agreed about the shoulder. It's all sacrificial brass at this point.

 

[neckturner]

Is there a reason for neck turning Alpha 6 GT brass?

I thought there would not be, and was checking to be sure. Then I discovered that this batch has a tapered neck thickness and became concerned, as it would create tapered holding force on the bullet.

 

[NiteQwill]

I thought there would not be, and was checking to be sure. Then I discovered that this batch has a tapered neck thickness and became concerned, as it would create tapered holding force on the bullet.

I can say, with almost 99.999% certainty, it doesn't matter on a target downrange. I have upwards of 13k rounds downrange in 6 GT (looking at my last boxes of Bergers sitting on my shelf, 2k left)... I have never turned necks. But if you find you need to, then you do you.

 

[neckturner]

Thinking about it, if I did go all the way to .013, that would give .269 OD which, if the chamber is SAAMI (I just took delivery of the reamer but do not have the dimensions and will do a chamber cast when everything comes back to me in a bunch of weeks), gives me .004 total, divided by 2 is .002 clearance. Which might be just fine given what I'm now becoming aware of for neck clearance. Food for thought.

 

[neckturner]

I have never turned necks. But if you find you need to, then you do you.

It's less about me doing me and more about I've never seen tapered neck thickness in Lapua brass. So I'm wondering if your neck thickness is relatively uniform and if tapered is either unusual or harmful.

On the first, I used the K&M with a dial gauge, you would use a ball micrometer if you have one.

 

[Willow]

If the tapered neck makes a difference, I sure as heck cannot tell on target. My 6GT is an absolute joy to shoot thanks to its ease of tuning and accuracy on target.

Unless you are running a tight neck chamber, I wouldn't worry with neck turning. I think most of the reamers out there for this cartridge are no-neck turn in the first instance.

 

[gqhoon]

No issues with the tapered neck on my 6GT OCD brass. Running it in an Alpha reamer chamber, which has a 0.274 neck.

 

[dgeesaman]

I thought there would not be, and was checking to be sure. Then I discovered that this batch has a tapered neck thickness and became concerned, as it would create tapered holding force on the bullet.

All brass has a ‘tapered’ holding force due to the stiffness added by the shoulder as well as the loss of stiffness caused by the mouth.

The additional taper in thickness means little to me. When I neck turn I’m trying to eliminate variations in thickness as you move radially around the neck. Based on that skim cut, your sample piece is exceptionally uniform.

 

[mikecr]

You need a ball mic to check thickness.
How much taper is there with new 308 brass (before necking down)?

 

[Tesoro]

Just an idea: can you make 6gt out of a Lapua case? Then you will be happy and case life is so long that it will be worth it. I am doing this for today's project converting Lapua 308 Palma srp into 6xc.

 

[reloaderguy]

FWIW, I have a bunch of early non-OCD Alpha 6GT and it is tapered too. I turned it all. I probably didn't need to. If you're final expanding as a last step there is probably less than no reason.

 

[Clancy]

All of my 6GT was tapered, and, like you, I had to go to .013 to clean it up. .005 clearance is no issue.

I have gone back to shooting a 6BR with Lapua. No need for all that other business.

 

[neckturner]

FWIW, I have a bunch of early non-OCD Alpha 6GT and it is tapered too. I turned it all. I probably didn't need to. If you're final expanding as a last step there is probably less than no reason.

All of my 6GT was tapered, and, like you, I had to go to .013 to clean it up. .005 clearance is no issue.

I have gone back to shooting a 6BR with Lapua. No need for all that other business.

Thanks to both of you, very helpful. Clancy, I'm increasingly hearing / reading that neck clearance being a bit larger than I'm used to (I have a fitted neck in 6mm PPC) is a non issue, so thanks for more corroboration.

FYI I've just been told by Alpha that this is "100% normal for our brass", and I'm to to just load and shoot. So when my barrel is finally in, I may try that but will eventually end up turning - uneven tension is uncomfortable.

Really appreciate all the replies. Especially since I was just banned at another otherwise-helpful forum for "Spam", when I certainly haven't issued any. EDIT: un-banned. some automated thing based on IP, administrator helped out once I found a way to contact him.

 

[Chris Edmondson]

Looking at the SAAMI drawing for 6mm GT, the neck is specified as .273 CYL which, from what I can find concerning the CYL nomenclature, means cylindrical. Since there isn't a specific dimension tolerance, and the drawing-level tolerance applies to "BODY DIA. -.008", I'm not sure what exactly to expect, I can see why you questioned your specimens though. One reason we choose to turn necks is a perceived level of imperfection in the mass-produced one's we buy; we're trying to fix something: Cylindricity, concentricity, runout and so on, why not add taper to the list, lol.

 

[neckturner]

why not add taper to the list, lol.

Exactly. How does one choose as bushing when the neck is tapered?

 

[Clancy]

@neckturner I wouldn’t worry about the extra clearance. In fact, might even shoot better than your fitted necks- probably would in the same chambering, obviously it would be a tall order for a GT to outdo a PPC.

If there’s anything I’ve learned in the last 10 years, and I mean anything, it’s that cute little clearances are not our friend. Guys are setting records of every kind with wide necks and heavy shoulder setback.

Don’t sweat it at all, and I have a bunch of loads for a GT if you get lost.

 

[mikecr]

How does one choose as bushing when the neck is tapered?

what sizes more due to thickness, springs back more due to thickness.
And pre-seating expansion aids in setting uniform interference.

Technically, all unturned cases are tapered in thickness from webs to mouths.
This is inherent to it's manufacture.

I can think of no reason that excess clearance is 'good'. The bullet is swinging in the wind before the neck expands to the chamber, so continued expansion is beyond ballistic influence.
Plenty of shooters have done well with reasonable and low clearances.