Can someone explain .308 headspace to me please?!

[Sheprador1973]

Good evening. I am trying to get my head around the concept of headspace and in particular how and why case shoulders get bumped.

For context I've been shooting and reloading about 6 years (centrefire) and have all the basics down. I shoot a Tikka .308 which is used exclusively for stalking so I don't need 'match grade' ammo or precision.

A few years ago I had a new experience whereby some home loads I'd put together misfired. Closer inspection (ruling out firing pin issues etc) revealed that some of the brass (nny) had had the shoulders inadvertently bumped back excessively. Looking into this is turned out to be a newly acquired die set that had a different (and unadvertised) die included while i inadvertently misused. Anyway, I chucked the main offenders, pulled the rest, shelved the brass and bought some new Lapua.

Looking at it today with a comparator set to hand, the fireformed Lapua (neck sized) comes in at an average of 1.621" on the Hornady gauge. The shelved brass upon measuring has a comparative average figure of 1.615". My questions are, if you can help/advise:

Is 0.006" enough to produce misfires (soft pin strike)?

Is the original brass salvageable/safe to reuse?

If shooting a bolt-action stalking rifle, fireforming the brass from new and neck sizing thereafter, do I need to concern myself with headspace? (With bullet, primer, powder, coal etc being kept the same)

And if so, how is it best done/checked and what does it achieve? (I'd based my initial assumptions on fire-formed, neck sized and trimmed brass being 'perfect' for my particular chamber, therfore not requiring extra attention).

If it helps, codes on the Lee dies are: (fl) LEE - 308 - 13 and (neck) LEE - 308 WIN - G9.

I hope that makes sense and that you might be able to explain the above to me. Thank you.

 

[VSS]

No idea, but good to see you getting back into the swing of things

 

[Sheprador1973]

No idea, but good to see you getting back into the swing of things

A very kind thing to observe and say. Sincerely, thank you

 

[Ronin]

Simplest way to visualise


Shoulder of case touches the chamber at a datum point and the bolt face is the second datum point

Case sizing (full length sizing) compressed the case to dimensions the same as or slightly smaller but within the tolerances of your chamber (if you are resizing correctly)

I always strip out firing pin when setting up my dies and work on the principle that the bolt handle should NOT drop under gravity on a re sized case but light single finger pressure only

Set your die’s incrementally to a point the bolt will close using light pressure only

Do not go past this

Do so and you are reducing the length bettween the two datum points and creating a situation where the case is not fully supported in the chamber

Hope this helps visualise the original question

 

[User00044]

Generally , we use the term "headspace" to mean two different things .
The first is a chamber measurement , the measurement is the distance from the breechface to a datum point on the shoulder as defined by SAAMI .
The second really describes the chamber fit of a cartridge . The measurement is similar in that it is again measured to a datum point on the case shoulder but from the case head(stamp).
If for example you have 0.002 " headspace , this would imply the shoulder of a fireformed case had been set back 0.002 " . I prefer to refer to this as " relative headspace ".
Lee full length dies are perfect for bump sizing .
0.006" should not cause light strikes.

 

[kenbro]

Hi,
I would do as Ronin says.
And depending on rifle make you might have to remove the ejector if it’s a plunger type to get any real feel when closing the bolt.
Check you fired/neck sized cases in the chamber using this method but the bolt will probable fall closed with gravity.
If you have any cases with excessive head space you could create a false shoulder on them, then load and shoot to form to your chamber.
Cheers, Ken.

 

[jcampbellsmith]

Sheprador1973

I recommend that you do not neck size any rounds that will be used for stalking.

Regards

JCS

 

[Cyres]

You could buy a case gauge. Willson and Lyman sell them. Correctly sized case will fit in. Easy to use whilst sitting in front of TV. Dauncey and Spud sell them.
D

 

[25 Sharps]

Good evening. I am trying to get my head around the concept of headspace and in particular how and why case shoulders get bumped.

For context I've been shooting and reloading about 6 years (centrefire) and have all the basics down. I shoot a Tikka .308 which is used exclusively for stalking so I don't need 'match grade' ammo or precision.

A few years ago I had a new experience whereby some home loads I'd put together misfired. Closer inspection (ruling out firing pin issues etc) revealed that some of the brass (nny) had had the shoulders inadvertently bumped back excessively. Looking into this is turned out to be a newly acquired die set that had a different (and unadvertised) die included while i inadvertently misused. Anyway, I chucked the main offenders, pulled the rest, shelved the brass and bought some new Lapua.

Looking at it today with a comparator set to hand, the fireformed Lapua (neck sized) comes in at an average of 1.621" on the Hornady gauge. The shelved brass upon measuring has a comparative average figure of 1.615". My questions are, if you can help/advise:

Is 0.006" enough to produce misfires (soft pin strike)?

Is the original brass salvageable/safe to reuse?

If shooting a bolt-action stalking rifle, fireforming the brass from new and neck sizing thereafter, do I need to concern myself with headspace? (With bullet, primer, powder, coal etc being kept the same)

And if so, how is it best done/checked and what does it achieve? (I'd based my initial assumptions on fire-formed, neck sized and trimmed brass being 'perfect' for my particular chamber, therfore not requiring extra attention).

If it helps, codes on the Lee dies are: (fl) LEE - 308 - 13 and (neck) LEE - 308 WIN - G9.

I hope that makes sense and that you might be able to explain the above to me. Thank you.

Lee FL dies do not allow you to size the case to the headspace of your rifle. They have to cam over to FL size, so you either return the cases to factory spec or you don’t really size the case at all, no inbetween.

Depending on the chamber of your rifle you could therefore be right on the lower limit of factory and your chamber could be on the max meaning you have excessive space between the case shoulder and the chamber shoulder. This can lead to light strikes of failure to fire.

Conventional wisdom is not to neck size for stalking ammunition in case you need a fast follow up. Reason being after enough firings the shoulder will be too far forward and the bolt will be difficult to close.

That said I neck size for most of my hunting rifles but I make sure I bump the shoulder back with an FL die (some of them Lee) around every third firing. This means I have never had an issue chambering a round when I need to.

The brass you have inadvertently bumped too far back will be fine to use. As you say fireform them and they will head space correctly again. Use the softest primer you have or if using a low pressure load (I.e. near min not max) just nudge the ogive into contact with the rifling. Which means you’ll hold the cartridge in place for the case to fireform. This is what a lot of wildcatters do to form cases. Don’t do this with a top end load due to the risk of the bullet with no jump pushing the pressures up.

 

[Sheprador1973]

Thank you guys, very helpful although will probably take a few re-reads to fully take in.

One thing that still confuses me. If I shouldn't neck size for stalking (for the well explained reasons above) and I want to keep the cases fireformed to the chamber (ie I don't FL size either) how does the case neck have the tension on the bullet upon the next reload? Or are we saying that most stalkers FL size after each firing? Apologies if I'm missing something very obvious.

 

[Sheprador1973]

You could buy a case gauge. Willson and Lyman sell them. Correctly sized case will fit in. Easy to use whilst sitting in front of TV. Dauncey and Spud sell them.
D

Sounds like it would make a lot of sense to invest in one of these. Thank you

 

[HandB]

Following on from Ronin's excellent advice, one thing you can do to confirm your die is sizing your cartridge case correctly is to stick a circle of 3M sticky tape on the base of the sized cartridge case. This tape is 2 thou thick so if the bolt handle becomes harder to lower compared to when there is no tape on the base of the cartridge case then you know you have sized it 2 thou smaller than chamber size. Details are here in this Erik Cortina video

 

[Cottis]

Thank you guys, very helpful although will probably take a few re-reads to fully take in.

One thing that still confuses me. If I shouldn't neck size for stalking (for the well explained reasons above) and I want to keep the cases fireformed to the chamber (ie I don't FL size either) how does the case neck have the tension on the bullet upon the next reload? Or are we saying that most stalkers FL size after each firing? Apologies if I'm missing something very obvious.

FL sizing does also size the necks so that adequate neck tension is realised to allow for successful bullet seating. Neck sizing only sizes the neck so tension is adequate to seat bullets but without sizing any of the rest of the brass case.

I FL size every firing.

Sorry, I just re-read your message (correctly this time ha ha) ignore the above.

You need to do some form of sizing after each firing. Fire forming brass blows it out to either match your chamber size or gets close to it. There will be some variations which are probably minor. You can test this with comparator equipment. You do not want brass sized to your exact chamber measurements as this is where you begin to encounter issues with easy chambering of cartridges. Something that is annoying and an issue if you need a quick second shot or even a third.

You could/should follow Ronin's advice or I have tended to find a piece of brass that shows difficulty in chambering but does so with a minimum of effort and then keep that back as a control for that particular rifles chamber and then I use it as a gauge to bump the shoulders back 2 thou on subsequent resizing sessions. My reloading box is full of either dummy cartridges or blown out cases minus 2 thou for gauges and control measurements for setting up seating dies etc.

 

[Steff]

Thank you guys, very helpful although will probably take a few re-reads to fully take in.

One thing that still confuses me. If I shouldn't neck size for stalking (for the well explained reasons above) and I want to keep the cases fireformed to the chamber (ie I don't FL size either) how does the case neck have the tension on the bullet upon the next reload? Or are we saying that most stalkers FL size after each firing? Apologies if I'm missing something very obvious.

So much has been said already. Much of it is true but not all of it.

Do neck size only as long as your bolt closes comfortably. If you have assorted brass with the same amount of firings from the same chamber they will also behave the same. Thus there‘s no danger of not being able to chamber a round during stalking.

Stop measuring! It won‘t get you anywhere. As soon as your brass won‘t chamber properly get out the FL sizing die and work your way down to the point where it will chamber. As a rule of thumb this will be a 1/8 turn up of the die from it touching the shellholder. A comperator will not help you to find this correct setting.
Again, only use assorted brass of the same brand, lot, chamber and firing cycle.

Don‘t ever oversize your brass! This will inevitably lead to case head separation; sooner or later, but it will.

 

[Sheprador1973]

So a neck sizing die doesn't touch the case shoulder at all...just reduces the case neck only to provide tension on the bullet?

Like the idea of the 'control' brass for reference Cottis

 

[jcampbellsmith]

So much has been said already. Much of it is true but not all of it.

Do neck size only as long as your bolt closes comfortably. If you have assorted brass with the same amount of firings from the same chamber they will also behave the same. Thus there‘s no danger of not being able to chamber a round during stalking.

Stop measuring! It won‘t get you anywhere. As soon as your brass won‘t chamber properly get out the FL sizing die and work your way down to the point where it will chamber. As a rule of thumb this will be a 1/8 turn up of the die from it touching the shellholder. A comperator will not help you to find this correct setting.
Again, only use assorted brass of the same brand, lot, chamber and firing cycle.

Don‘t ever oversize your brass! This will inevitably lead to case head separation; sooner or later, but it will.

This breaks rule 1 of reloading - follow the same process every time.
Regards
JCS

 

[Steff]

This breaks rule 1 of reloading - follow the same process every time.
Regards
JCS

No, you're misreading the rules.
It goes, follow the same procedure through every cycle.
Different conditions of the brass require different treatment. This in an attempt to restore near equal conditions across the firing cycles.

 

[Sheprador1973]

So much has been said already. Much of it is true but not all of it.

Do neck size only as long as your bolt closes comfortably. If you have assorted brass with the same amount of firings from the same chamber they will also behave the same. Thus there‘s no danger of not being able to chamber a round during stalking.

Stop measuring! It won‘t get you anywhere. As soon as your brass won‘t chamber properly get out the FL sizing die and work your way down to the point where it will chamber. As a rule of thumb this will be a 1/8 turn up of the die from it touching the shellholder. A comperator will not help you to find this correct setting.
Again, only use assorted brass of the same brand, lot, chamber and firing cycle.

Don‘t ever oversize your brass! This will inevitably lead to case head separation; sooner or later, but it will.

Really glad you posted this, for my sake but also that of others with less experience. It is easy to assume, even when having digested the literature that accompanies a die set, that FL sizing ONLY sets your case back to factory spec. Little to nothing is mentioned about different degrees of FL sizing and/or using your own chamber as the primary reference point.

I'll get the rifle out tomorrow and follow the thorough advice given above. In relation to the aforementioned shelved brass, if it is oversized (bit of a confusing term as implies 'bigger') as suspected, the bolt will drop under gravity alone?

Thanks very much...will report back.

 

[Cottis]

So much has been said already. Much of it is true but not all of it.

Do neck size only as long as your bolt closes comfortably. If you have assorted brass with the same amount of firings from the same chamber they will also behave the same. Thus there‘s no danger of not being able to chamber a round during stalking.

Stop measuring! It won‘t get you anywhere. As soon as your brass won‘t chamber properly get out the FL sizing die and work your way down to the point where it will chamber. As a rule of thumb this will be a 1/8 turn up of the die from it touching the shellholder. A comperator will not help you to find this correct setting.
Again, only use assorted brass of the same brand, lot, chamber and firing cycle.

Don‘t ever oversize your brass! This will inevitably lead to case head separation; sooner or later, but it will.

A comparator compares. It can absolutely assist you in sizing brass to an exact standard relative to another piece of brass. That is entirely the point.

And don't use assorted brass. Use identical brass from the same batch.

 

[Edinburgh Rifles]

This term “factory spec”….
Which factory is this?

Think of dies and more importantly the brass that comes out of them, and chambers …as feet and shoes
No pair are alike
Your size 9 feet may not fit size 9 Nike shoes..but they might fit Adidas

You FL size a case in two different dies you will get two different length cases from head to shoulder datum point
You try to chamber a fired case in two rifles, it may chamber in one but not the other.

Factory spec is within a tolerance
Tight chambers at one end and loose dies at the other or vice versa can create issues

Do NOT assume a FL die returns anything to any spec
Size your brass to YOUR chamber
Do not wind it down and cam over assuming it’s will be fine.
Your size 9 chamber may not match the size 9 die

Size your brass so it only just allows a bolt to close without undue pressure (ideally with the firing pin spring removed)

Neck sizing is not an issue if you test chamber all rounds before you use them
You should do this anyway, if you have never had a round fail to chamber or get stuck before you are lucky.
I have had factory anomalies with bulged necks and other brass anomalies that don’t chamber