Neck Turning in SAAMI Chamber: Unwise?

[Phil3]

I don't really expect that neck turning for a SAAMI spec chamber will produce any additional accuracy, but do wonder if it could shorten brass life. For instance, consider the neck dimensions for my AR-15 with Krieger barrel chambered in 223 Remington. Before anyone dismisses the idea of neck turning for an AR, please understand this is my only centerfire rifle I have right now, but do have a Howa 223 Remington bolt action (w/SAAMI chamber) on its way back to me from a gunsmith in the next week or so. These question then, are more for what I will do with the Howa. I don't expect to do neck sizing with the AR, unless someone tells me it does provide a benefit.

Fired Brass: .2535"
Resized Brass: .2450"

This is a "blow-out" of the brass during fire forming of .0085".

The neck thickness ranges from .011 to .013. If I used a neck turner to take most of the high spots off, I might shrink the average neck diameter by say, .0015". That would mean the resized neck diameter is no longer .2450, but .2435.

This is a now a blow-out of the brass during fire forming of .0100 vs the previous .0085. That is just more working of the brass. Worse, the brass is now thinner due to the neck turning, leading to potentially even more brass fatigue.

Seems to me I should avoid neck turning until I have a rifle that has a tighter neck. Is my logic flawed?

Thank you.

Phil

 

[Beau]

I did it for a SAAMI-chambered .223 and it was a total waste of time.

 

[Alex Wheeler]

I turn brass if I am using a die that has a neck bushing and no expander. If I wanted to use un turned brass I would use an expander. You could turn your brass, it wont hurt. Will it shorten the life of the brass? Probably a little.

 

[jlow]

This is a question that gets asked hundreds of times. There are at least three reasons to neck turn brass:

1) To adjust the case for a tight chamber rifle.
2) To give you better concentricity – only a slight effect unless your necks are way off.
3) To give more consistent neck tension – this would be the main reason to neck turn for rounds shot out of a SAAMI chambered rifle.

Consistent neck tension gives consistent MV which would be important really only for long distance shooting i.e. 600 yards or greater not short distance.

As for the life of the brass, I would agree with zfastmalibu that the effects are small especially if you load hot since the primer pockets will loosen long before you get neck splits. If you are worried about neck splits, anneal after every firing and that will have more of a positive effect.

 

[SmokinJoe]

zfast & jlow have it pegged pretty well IMO. However, your analysis is flawed. Measuring the fired brass is correct, but measuring resized brass is not the comparison you are looking for. Instead, you need to compare the fired brass neck diameter to loaded round neck diameter. I think you will find loaded round neck diameter to run close to .248 for domestic brass (Lapua will be a bit larger), and it looks as though you probably have a .255 neck diameter in your chamber, which is pretty standard SAAMI spec. If you turn all your brass to clean up 80-90% and use a bushing type sizer w/o expander, you should get better bullet seating consistency (which you can control with different sizing bushings), and you may get more concentric loaded ammo, also. By turning the brass to make the necks more consistent, you will add a thousandth or so extra stretch when firing, and that will maybe have a minor effect on brass life. If you re-anneal every 3 or 4 firings you can still make that brass live a long time in a bolt gun.

 

[Phil3]

This is a question that gets asked hundreds of times. There are at least three reasons to neck turn brass:

1) To adjust the case for a tight chamber rifle.
2) To give you better concentricity – only a slight effect unless your necks are way off.
3) To give more consistent neck tension – this would be the main reason to neck turn for rounds shot out of a SAAMI chambered rifle.

Consistent neck tension gives consistent MV which would be important really only for long distance shooting i.e. 600 yards or greater not short distance.

As for the life of the brass, I would agree with zfastmalibu that the effects are small especially if you load hot since the primer pockets will loosen long before you get neck splits. If you are worried about neck splits, anneal after every firing and that will have more of a positive effect.

I generally understand the benefits of neck sizing. Please see the data below.

Considering a loaded round vs a fired round: Assume .001 removed from neck wall (shrinks neck OD by .002).

No-turn Neck: Loaded = .2480. Fired = .2535. Difference = .0055.
Turned Neck: Loaded = .2460. Fired = .2535. Difference = .0075.
Add'l Neck Blow-out = .0020".

My question was whether the brass blowing out an additional amount (.002") would materially affect the life of the brass. Additionally, would a sudden brass stretch of .0075" be pushing the limits of what the brass could tolerate without splitting or failing. Clearly, .0055" is fine, because no brass of mine has failed when subjected to that level of blow-out.

I don't have enough experience to play around with hot loads, but won't be doing so unless best accuracy is found there. I expect case failures to probably happen in places other than those generally specific or more commonly found with hot loads.

Phil

 

[jlow]

I have never seen a study which looks at very slight differences in neck thickness and its effect on brass life, so I cannot honestly give you a scientific answer.

What I can tell you is I turn all my brass (223 and 308) and have never seen a single piece of my brass with a neck split but I have seen lots of loose primer pockets. I do anneal every time since I have a machine and so is easy.

Perhaps I am lucky, but more likely is neck splits are not something that I should worry about. The way I look at this, the neck is more likely to split when the brass becomes brittle or what we call work harden from being fired and not from being thinner or having to move that additional 2 thousands.

 

[Phil3]

zfast & jlow have it pegged pretty well IMO. However, your analysis is flawed. Measuring the fired brass is correct, but measuring resized brass is not the comparison you are looking for. Instead, you need to compare the fired brass neck diameter to loaded round neck diameter. I think you will find loaded round neck diameter to run close to .248 for domestic brass (Lapua will be a bit larger), and it looks as though you probably have a .255 neck diameter in your chamber, which is pretty standard SAAMI spec. If you turn all your brass to clean up 80-90% and use a bushing type sizer w/o expander, you should get better bullet seating consistency (which you can control with different sizing bushings), and you may get more concentric loaded ammo, also. By turning the brass to make the necks more consistent, you will add a thousandth or so extra stretch when firing, and that will maybe have a minor effect on brass life. If you re-anneal every 3 or 4 firings you can still make that brass live a long time in a bolt gun.

I understand why you feel I should measure the loaded round. However, my purpose was to look at total brass working, and what negative impact additional brass working (through thinner necks) would have on brass life. This is why I looked at fired dimension (the max) vs what came out of the press. In truth, I should be looking at ALL that happens to neck. As it turns out, the total amount of brass working is the same with neck turned or no-turn. See below. Numbers in parentheses are the difference between the measurement on that line and the measurement on the line above.

No-Turn Neck
Fired Case: .254
FL Size (no expander): .240 (.014)
Size Back w/expander: .246 (.006)
Load Round: .248 (.002)
Fired Case: .254 (.006)
Total of Dimensional Changes: .028

Neck-Turned (cut wall thickness by .001)
Fired Case: .254
FL Size (no expander): .240 (.014)
Size Back w/expander: .244 (.004) - Smaller OD than no-turn because neck walls are thinner.
Load Round: .246 (.002)
Fired Case: .254 (.008) - Larger than no-turn because smaller OD neck travels further to fill chamber.
Total of Dimensional Changes: .028

Guess I answered my own question, unless my math is flawed or something else amiss (very possible!).

Phil

 

[Phil3]

I have never seen a study which looks at very slight differences in neck thickness and its effect on brass life, so I cannot honestly give you a scientific answer.

What I can tell you is I turn all my brass (223 and 308) and have never seen a single piece of my brass with a neck split but I have seen lots of loose primer pockets. I do anneal every time since I have a machine and so is easy.

Perhaps I am lucky, but more likely is neck splits are not something that I should worry about. The way I look at this, the neck is more likely to split when the brass becomes brittle or what we call work harden from being fired and not from being thinner or having to move that additional 2 thousands.

Hmmm..., sounds like I need annealing equipment, especially if I want the new Lapua brass I just got to live a long and healthy life. Time to explore annealing tools!

Phil