Case neck thickness variance

[dm.oakes]

I'm curious as to what folks deem as acceptable variance in neck thickness?

This is .308 Lapua LR primer brass being used in my F/TR rifle. The chamber was cut from a .308 Match reamer from PTG with a .341 neck. The variance I'm seeing is currently .001-.003 variance in the neck thickness.

Trying to determine if time/cost benefit is worth the net gain from turning these necks with the variance I'm seeing.

 

[P1ZombieKiller]

I do not shoot F/TR, but in shortrange BR, that might as well be a mile.

I would turn ALL necks in ALL competition guns.

 

[artbosco]

I'm curious as to what folks deem as acceptable variance in neck thickness?

This is .308 Lapua LR primer brass being used in my F/TR rifle. The chamber was cut from a .308 Match reamer from PTG with a .341 neck. The variance I'm seeing is currently .001-.003 variance in the neck thickness.

Trying to determine if time/cost benefit is worth the net gain from turning these necks with the variance I'm seeing.

With my tight neck chambers I have to turn my Lapua brass in order to get the case neck to fit inside the chamber. For example, my 6PPC has a .262" neck chamber. I turn so a loaded cartridge with the bullet seated measures .260" OD at the bullet's pressure ring [if it has one]. However, I'm willing to except no more than plus or minus .0003" [3/10,000ths] either side of that figure .2603" or .2597". I want a total clearance of .002" for safety [.001" on each side]. I won't go less than .0017" total [.2603 + .0017 = .262"] Hope this helps.

P.S. If you have a .341" neck chamber I recommend you turn to at least an OD, with a bullet seated, of .339" regardless of the case neck thickness dimension when pulled from the box.

 

[Lapua40X]

I turn 'em for .001 - .0015 neck clearance and try to get .001 - .005 runout; sometimes have to settle for .0015. .003 is not, IMO, acceptable.

 

[effendude]

A couple things. Ideally you want about .003 to .004 clearance between your loaded round and the chamber. Measure a loaded round's diameter and compare that to your chambers dimension. All brass will benefit from turning. You don't have to clean up 100%, 70% is a good start. You are just making the neck dimensions more uniform so you have consistent neck tension. My F-TR rifles have .341 necks and I skim turn for .004 clearance with a loaded round diameter or .337. I don't measure neck wall thickness.

Scott

 

[fdshuster]

For my .339" chamber necked 308, I'm turning my Lapua to .014", for a loaded round neck diameter of .336". Just a one pass, light cleanup cut.

 

[amlevin]

I have a hard time grasping the idea that one can size a case with uneven neck thickness and expect the bullet to be held concentric. The sizing die is making the outside of he case concentric but the uneven neck thickness will result in an eccentric inner "bore" of the case neck.

I turn ALL cases just to make sure the neck is concentric, inside and out, not to fit the chamber.

It pays off if you're looking for the most accuracy possible.

If "good enough" is your goal then don't bother.

 

[Martin52]

I have a hard time grasping the idea that one can size a case with uneven neck thickness and expect the bullet to be held concentric. The sizing die is making the outside of he case concentric but the uneven neck thickness will result in an eccentric inner "bore" of the case neck.

Unless you're sizing with a Lee Collet die - it will push the inconsistencies to the outside of the case neck leaving the "bore" of the neck perfect, it's good for resizing unturned brass.

Martin

 

[Martin52]

I'm curious as to what folks deem as acceptable variance in neck thickness?

This is .308 Lapua LR primer brass being used in my F/TR rifle. The chamber was cut from a .308 Match reamer from PTG with a .341 neck. The variance I'm seeing is currently .001-.003 variance in the neck thickness.

Trying to determine if time/cost benefit is worth the net gain from turning these necks with the variance I'm seeing.

My recent purchases of new lapua 308 brass have seen neck thicknesses around 0.0145 - 0.015 but not much more. maybe I got lucky. Anyway, I still find I have to turn my cases down to 0.0140 to minimise neck thickness variation to <0.0002.

Martin

 

[Erik Cortina]

To the OP:

What tool are you using to measure your necks?

Lapua40X: .001-.005" runout? Was that a typo?

 

[dm.oakes]

Eric - I'm utilizing a Redding Case Neck Gauge

Martin - I've been using a Lee Collet die for all of my neck sizing.

 

[dm.oakes]

The brass from Lapua will fit this chamber without having to turn the necks (these are on their 3rd firing). A loaded round measures .3390, so I've got plenty of clearance without turning.

 

[Martin52]

Martin - I've been using a Lee Collet die for all of my neck sizing.

You should be fine then using your LCD for unturned necks for the reasons mentioned.

Having said that, I personally turn to 0.0140 and use a FLS bushing die. From time to time eg fireformig new brass before n/turning, I would use the LCD.

Martin

 

[amlevin]

I have a hard time grasping the idea that one can size a case with uneven neck thickness and expect the bullet to be held concentric. The sizing die is making the outside of he case concentric but the uneven neck thickness will result in an eccentric inner "bore" of the case neck.

Unless you're sizing with a Lee Collet die - it will push the inconsistencies to the outside of the case neck leaving the "bore" of the neck perfect, it's good for resizing unturned brass.

Martin

I have to admit that I do like the Lee Collet Die. That said, I find that I have to anneal my brass frequently in order to get the uniformity of neck tension I want.

Sure wish Lee offered a set of mandrels in various diameters so one could adjust neck tension without having to buy several standard mandrels then grind, file,sand, or ?? them to the size you want.

 

[jsthntn247]

If your getting .003 thickness I would turn them all to the diameter of the worst case . If it was only a few that far off I would cull them and go to the next diameter down. It's really not going to matter just make them all consistent and if you have to size down more than.004 from fired diameter do it in two steps. Thats the reason I also got a reamer with a .339 neck and turn to .01375 for a .3355 loaded diameter.

 

[masterblaster1]

I am also a fanboy of the LCD, I understand you can have them cut a custom mandrel for a fee. I am just getting to the turning stage of my new found OCD, after finding this site and 30 years of reloading experience.

I have a hard time grasping the idea that one can size a case with uneven neck thickness and expect the bullet to be held concentric. The sizing die is making the outside of he case concentric but the uneven neck thickness will result in an eccentric inner "bore" of the case neck.

Unless you're sizing with a Lee Collet die - it will push the inconsistencies to the outside of the case neck leaving the "bore" of the neck perfect, it's good for resizing unturned brass.

Martin

I have to admit that I do like the Lee Collet Die. That said, I find that I have to anneal my brass frequently in order to get the uniformity of neck tension I want.

Sure wish Lee offered a set of mandrels in various diameters so one could adjust neck tension without having to buy several standard mandrels then grind, file,sand, or ?? them to the size you want.

 

[gilream]

I have a hard time grasping the idea that one can size a case with uneven neck thickness and expect the bullet to be held concentric. The sizing die is making the outside of he case concentric but the uneven neck thickness will result in an eccentric inner "bore" of the case neck.

Unless you're sizing with a Lee Collet die - it will push the inconsistencies to the outside of the case neck leaving the "bore" of the neck perfect, it's good for resizing unturned brass.

Martin

I have to admit that I do like the Lee Collet Die. That said, I find that I have to anneal my brass frequently in order to get the uniformity of neck tension I want.

Sure wish Lee offered a set of mandrels in various diameters so one could adjust neck tension without having to buy several standard mandrels then grind, file,sand, or ?? them to the size you want.

amlevin...Lee will sell you undersized mandrels for 5 bucks apiece...you specify the caliber and diameter that you want. They will also sell you an oversized mandrel for $10.
http://leeprecision.com/custom-undersized-mandrel.html

 

[Alex Wheeler]

I turn my brass on all my serious rifles. I expect +/- .0001" If I had to use un-turned brass I would sort to batches or +/- .0005 and use and expander to uniform the i.d. of the cases. But it seems so much quicker and easier to just turn them and be done with it.

 

[dm.oakes]

thank you everyone for your input and suggestions.

 

[Syncrowave]

I don't mean to hijack thread, but I'm new to neck turning and this seemed like a good thread to ask for advice.

I bought a bunch of cheap new Black Hills 6.5/284 cases and necks seem to run between .0156" and maybe .0172" thick.

Seems like a lot of people say not to take enough brass off to make the necks totally uniform thickness but to turn such that maybe 1/2 or 2/3 of the circumference of the neck is shaved.

So if I set my neck turner to give a max thickness of, say, .0165" and it went down to .0156" sometimes, would most of you consider that a decent starting point? (In other words, max thickness variation of .0009")?

I should note that I'm not a super good shooter / match competitor yet, just trying to work my way into better accuracy. So I don't need to go "all out" yet, since rifle probably shoots a lot better than me at this point.

(Also, unfortunately, I don't know the exact diameter of my chamber neck yet.)

Thanks for any advice.


P.S. Also - I should turn my brass when new, not once fired, right? And if I use new brass, how do I get the neck over the mandrel of my Nielson neck turner? New brass won't fit over the mandrel, and full-length sized brass won't fit, either (I have Redding conventional FL and neck-sizing dies, not mandrel / bushing type.)