What neck thickness when turning? 223, 308, 6 Dasher, 6.5 x47, 284 Win, 300 WSM?

[Patriot007]

If you just “clean up” the necks for use in a factory chambered rifle, do you think the accuracy rewards would be evident?

I say yes. Keep in mind that the word Turning should actually be TRUEING. ( Like Turning a brake rotor on a car.) It definitely made a difference in my ED,SD, and Averages. Not to mention the groups sizes. It's all about eliminating the variables. Opinions vary on this subject, and this is just mine. "It works for me."

 

[Dwubyd]

I have run into a problem with my 223 Ackley Imp. The chamber is around 0.254". I am guessing this because fired brass measures 0.253" and the common spec for reamers is 0.254-0.255".

The problem is that I turned my necks to a bit over 0.012". So bullet plus neck is 0.2230+02 x 0.12 = 0.2475 ish. So neck to chamber clearance is around 0.006". If I use the sizing process of bushing die, then mandrel with 0.002" of sizing at each step and 0.002" neck tension, I end up with the following:

Bullet diameter: 223
Mandrel: 221
Bushing: 244 (221+25 -2 = 244)
Fired brass: 253

So the sizing step is from 253 to 244. This large step results in flared necks and undersized diameter (believe it or not). So as a previous poster mentioned, I have to size in two steps.

So neck turning can have consequences, especially in factory rifles or SAAMI spec chambers because they are made to suit all brass and ammo, up to the thickest of necks.

I am considering switching to Lapua brass and not neck turning. to reduce the amount of sizing.

For context, it is a PRS rifle and shoots 0.3-0.4" for 5 shots at 100m when it is shooting well.

Another consideration is what I call "low hanging fruit". You have to find the one factor that is affecting accuracy the most and focus on that. No point turning necks if another factor is having a larger affect on group sizes. You won't see any difference. The list of possible factors is long: powder, amount of powder, projectile, barrel twist rate, primer, seating depth, brass, etc. Then add in the rifle itself: scope issues, scope mounting issues, bedding, barrel quality, the support system (bipod, bench rests, bags). Finally the meat bag pulling the trigger.

Edit: After some internet research, I found that Lapua brass is not much thicker than ADI. Norma is though.

 

[Straightshooter1]

Anyone familiar with the term "thin and win" and where it came from and why?

If so, is it true that many pro's like to use thinly turned necks as it's claimed to improve their results?

 

[SixFive]

There is no reason to neck turn for factory rifle SAMMI chambers. That is just my 2 cents. In fact you could actually do more harm than good if you do ANYTHING other than a cleanup pass, but it is not needed.

 

[SixFive]

Anyone familiar with the term "thin and win" and where it came from and why?

If so, is it true that many pro's like to use thinly turned necks as it's claimed to improve their results?

I think it is all about neck tension at this point, in many years of reloading I have seen most rifles respond well to about .002 neck tension. The exception is solid copper bullets, they seem to like a mild crimp for whatever reason (ESPECIALLY HAMMER BULLETS!)

 

[Bronsin]

I've turned necks for every factory chambering that I've owned, and never had a problem with any of them. Making the clearance .001 or .002 smaller in an already big chamber meant nothing. It works the brass more than I would have liked, but they always shot better with turned necks. The .308 and .22-250 have way more clearance than needed, but no one complains about overworking the brass when sizing either of them.

 

[Straightshooter1]

There is no reason to neck turn for factory rifle SAMMI chambers. That is just my 2 cents. In fact you could actually do more harm than good if you do ANYTHING other than a cleanup pass, but it is not needed.

What harm would you say it can do?

I took a small batch of Federal .308 brass and turned them down to .0125" and was surprised that they performed really well (still at .002 "neck tension"), better than those skimmed to .0140" with .001" "neck tension". And yes, turning them thin will work the brass more, but annealing after every firing seems to mitigate that a lot.

You might be right to some extent about it being an issue for "neck tension". But I have a feeling that there's more to it than that, like. . . the thinness lets the necks expand faster, sealing off the chamber faster (just my theory).

 

[Explorer1]

Any thoughts on velocity differences due to variations in neck thicknesses?
I shoot benchrest. Most of my Lapua 30BR cases are cut to 0.0098 neck thickness but I recently got a Garmin chronograph and found SDs of about 20fps and expected/wanted less variation.
So I started measuring neck thicknesses and found some variation. Most varied .0098-.0095. The extreme was one case was actually 0.0085. My own fault of course, these brass were my first trip into turning about 15yrs ago; I still rarely do it as the brass simply lasts. Now have over 2,500 rds down the tube using <150 pcs of brass. Haven't started experimenting with annealing.
I loaded 10 rds with brass having consistent necks of +0.0000, -0.0003 and found a SD of 9.8 fps. Haven't noticed any real difference in accuracy, precision, or consistency on target so I could be overkilling it.

Has anyone else had a similar experience?

 

[SixFive]

What harm would you say it can do?

I took a small batch of Federal .308 brass and turned them down to .0125" and was surprised that they performed really well (still at .002 "neck tension"), better than those skimmed to .0140" with .001" "neck tension". And yes, turning them thin will work the brass more, but annealing after every firing seems to mitigate that a lot.

You might be right to some extent about it being an issue for "neck tension". But I have a feeling that there's more to it than that, like. . . the thinness lets the necks expand faster, sealing off the chamber faster (just my theory).

I was thinking of thinning of the brass beyond what was needed to clean it up on these SAMMI chambers. I do clean up the neck to make it true but this usually still leaves me with .015 neck thickness on my Lapua brass. I always feared turning to much on these SAMMI chambers would contribute to neck splitting and a short brass life. I shoot most of the Nosler calibers and brass costs so much, I am just careful to make it last. I think annealing is a good idea and do it after each firing also.

In the end it is mostly opinion and some experience, but it is fun to discuss and learn what others do!

Interestingly enough I have experienced what Bronsin mentioned above in some rifles it does assist accuracy even with a SAMMI chamber, but in others I have seen no difference, your mileage may very.​

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[MikeRu]

Interested in what is commonly done for 223, 308, 6 Dasher, 6.5 x47, 284 Win, 300 WSM. Not OD but thickness of the wall after turning.

As thick as possible considering the following.

Before turning or uniforming a case I do this math to pick a wall thickness:
bullet diameter + 2X (neck wall) =
chamber neck diameter minus desired clearance

I use a clearance of 4 mostly. I use enough clearance that a bullet will drop into a fired case mouth.

After turning a test case, seat a bullet in the turned case and confirm that the final neck OD after seating a bullet, measured with a micrometer, is actually equal to [chambered neck diameter minus desired clearance].

You could also make sure it chambers in the rifle.