Necking down 308 to 7mm08

Hey chaps.
So a friend in the US has sent me 1,000 rounds of 308 brass (once fired, fully resized and tumbled and ready to use). I'm going to be flicking some of them off... but I thought since some of my brass is getting a little tired, I'd like to have a crack at necking some of it down.

Now on another forum I'm on some of the guys reckon I can just neck them down and it's done. Others are talking about annealing the brass to make it last longer (which I've never done) and talking about reaming the neck.

Anyone here done it? Any of you seasoned reloaders got any tips? :)

Cheers guys.

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Originally Posted by RimfireNZ

Hey chaps.
So a friend in the US has sent me 1,000 rounds of 308 brass (once fired, fully resized and tumbled and ready to use). I'm going to be flicking some of them off... but I thought since some of my brass is getting a little tired, I'd like to have a crack at necking some of it down.

Now on another forum I'm on some of the guys reckon I can just neck them down and it's done. Others are talking about annealing the brass to make it last longer (which I've never done) and talking about reaming the neck.


Anyone here done it? Any of you seasoned reloaders got any tips? :)

Cheers guys.

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Size a few down & check the neck diameter with a projectile in it against a "normal" one.

You should be GTG, another check is to make sure a projectile will fit easily into a fired case before it is sized.

If either of those don't measure up you will need to neck turn them, but if your rifle has a factory chamber that most likely won't be needed.

just run it through the F/L 7mm08 die,seat a projectile,check the neck dia.but should be good to go.

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Originally Posted by Kiwi Greg

Size a few down & check the neck diameter with a projectile in it against a "normal" one.

You should be GTG, another check is to make sure a projectile will fit easily into a fired case before it is sized.

If either of those don't measure up you will need to neck turn them, but if your rifle has a factory chamber that most likely won't be needed.

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Thanks KiwiGreg.
Beauty then. If all goes well with my testing I'm going to be swimming in ammo shortly :)

Probably ok but NOT always :x_x: Damn near blew up my CDL doing exactly that with PMC brass

Compare the neck diameter of a loaded case to a once fired one. If the loaded case is smaller then g-t-g

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Originally Posted by Cyclist

Probably ok but NOT always :x_x: Damn near blew up my CDL doing exactly that with PMC brass

Compare the neck diameter of a loaded case to a once fired one. If the loaded case is smaller then g-t-g

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Jeez... lucky you're alright. What could cause it to blow up?

I normally run quite a hot load in my 7mm... so I'll have to back this way out to a lower pressure load for testing. I don't want to blow myself up :s

if the neck is too thick and it's a tight chamber it can cause excessive neck tension and a pressure spike. the advice the others have given is to check this

Don't forget to check/trim overall length 2.01".
Chamfer. Excess length is the issue that will potentially give you the pressure spike as well.

What everyone else said above. I sized down 308 fed brass to 243.
Just got away with it with no neck turning.

Sent from my GT-S5360T using Tapatalk 2

As above for resizing 308 to 7-08.
Case length and neck diameter should be double checked before firing.

Annealing brass is a very simple process that can be accomplished quickly with minimal equipment.

Check out some of the You tube videos on this subject and give it a go.

It's a handy skill for the reloader to learn.

I use this method with very good success, except I air cool the brass.
Water cooling is ok but then you have to dry out your cases before reloading.

Annealing Brass in HD - YouTube

Here's a much more sophisticated annealing set up which accomplishes the same thing.

http://www.youtube.com/watch?v=yec8Yy3fEdg

Cheers
Pete

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Originally Posted by P38

As above for resizing 308 to 7-08.
Case length and neck diameter should be double checked before firing.

Annealing brass is a very simple process that can be accomplished quickly with minimal equipment.

Check out some of the You tube videos on this subject and give it a go.

It's a handy skill for the reloader to learn.

I use this method with very good success, except I air cool the brass.
Water cooling is ok but then you have to dry out your cases before reloading.

Annealing Brass in HD - YouTube

Here's a much more sophisticated annealing set up which accomplishes the same thing.

Annealing brass cases,. - YouTube

Cheers
Pete

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Thanks P38. So from what I've read and seen on YouTube about annealing its to release the tension in the brass and make it less brittle? That about right? Also apparently air and water cooling can have pretty different results. Based on this thread I don't think it would be needed but I'll do more reading and see.

I'd like to possibly convert my 223 to a 17-223 in the future so any little reloading tricks I can add to my collection like that will definitely get played with.

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Originally Posted by RimfireNZ

Thanks P38. So from what I've read and seen on YouTube about annealing its to release the tension in the brass and make it less brittle? That about right? Also apparently air and water cooling can have pretty different results. Based on this thread I don't think it would be needed but I'll do more reading and see.

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Annealing returns the brass grain structure back to its condition prior to being work hardened. Taking .308 brass and sizing it down to 7mm08 you have to plastically deform the neck i.e. deform it past the point it elastically returns. You can also plastically deform your case neck in firing it (case neck expands to the chamber neck diameter then contracts a little) and then sizing it back to be reloaded again (neck diameter is reduced to allow seating of the projectile with some tension). This plastic deformation work hardens the material, too much work hardening and the material becomes brittle and will easily break. Think of it like a paper clip that you bend a few times until it breaks... this is work hardening.

Plastic deformation deforms the material grain structure. The brass grain structure has to stretch and elongate to allow for the deformation, too much of this and the grain structure will crack. Heating the material up above its annealing temperature (but below its melting temperature) will allow the grain structure to re-crystallize (return to its pre-deformed structure).

Air cooled vs water cooled. Water cooling rapidly cools the brass compared to air cooling. The more rapid the cooling the harder the material ends up... and the less ductility it has.

Personally I resize .308 brass down to .260 and I have not found the need to anneal it yet. That said the chamber in my .260 is tighter than the SAAMI spec and I have to neck turn my re-sized brass. As a result I run very close tolerances between my chamber neck diameter and my loaded brass neck diameter. In running such close tolerances the neck on my brass does not go through much deformation either when it is fired or when I neck size it to be reloaded. Some of my brass has been reloaded nearly 10 times now and I have yet to throw one out.

call me lazy but if it was me id sell the 308 brass and buy a heap of 7-08 brass!

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Originally Posted by savage270

call me lazy but if it was me id sell the 308 brass and buy a heap of 7-08 brass!

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Good thinking Batman.

Theres always an easier soultion wating in the wings.

Necking down 308 brass to 7-08 is a simple process but it still leaves one issue that concerns me.

No matter what calibre the case ends up as, it will always be head stamped 308. :(

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Originally Posted by Cyclist

Probably ok but NOT always :x_x: Damn near blew up my CDL doing exactly that with PMC brass

Compare the neck diameter of a loaded case to a once fired one. If the loaded case is smaller then g-t-g

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You answered your own question here. PMC. Shit. Unless something amazing has happened it's never been good brass.

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Originally Posted by Gillie

Annealing returns the brass grain structure back to its condition prior to being work hardened. Taking .308 brass and sizing it down to 7mm08 you have to plastically deform the neck i.e. deform it past the point it elastically returns. You can also plastically deform your case neck in firing it (case neck expands to the chamber neck diameter then contracts a little) and then sizing it back to be reloaded again (neck diameter is reduced to allow seating of the projectile with some tension). This plastic deformation work hardens the material, too much work hardening and the material becomes brittle and will easily break. Think of it like a paper clip that you bend a few times until it breaks... this is work hardening.

Plastic deformation deforms the material grain structure. The brass grain structure has to stretch and elongate to allow for the deformation, too much of this and the grain structure will crack. Heating the material up above its annealing temperature (but below its melting temperature) will allow the grain structure to re-crystallize (return to its pre-deformed structure).

Air cooled vs water cooled. Water cooling rapidly cools the brass compared to air cooling. The more rapid the cooling the harder the material ends up... and the less ductility it has.

Personally I resize .308 brass down to .260 and I have not found the need to anneal it yet. That said the chamber in my .260 is tighter than the SAAMI spec and I have to neck turn my re-sized brass. As a result I run very close tolerances between my chamber neck diameter and my loaded brass neck diameter. In running such close tolerances the neck on my brass does not go through much deformation either when it is fired or when I neck size it to be reloaded. Some of my brass has been reloaded nearly 10 times now and I have yet to throw one out.

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Great explanation thanks Gillie.
So if I wanted to get the most out of my brass, I'd anneal the cases AFTER being sized down to 7mm, then air cool them (so they're not as brittle as water cooling), then bob's my uncle (after all the safety checks)?

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Originally Posted by savage270

call me lazy but if it was me id sell the 308 brass and buy a heap of 7-08 brass!

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Yeah that's an option, but I'm wanting to add another reloading skill to my toolkit.

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Originally Posted by RimfireNZ

So if I wanted to get the most out of my brass, I'd anneal the cases AFTER being sized down to 7mm, then air cool them (so they're not as brittle as water cooling), then bob's my uncle (after all the safety checks)?

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Yep, that would be my plan. :thumbsup: I would check the case neck diameter and case length after you anneal them.

It is marginal whether you need to anneal when necking 308 down to 7mm. I would skip that stage. Maybe anneal after 5 reload cycles. If you are getting no split necks (and you shouldn't) and good accuracy (consistant neck tension) all is good. Will depend more upon the life of the brass after you start using it - how sloppy is you chamber at the neck, how much work you do to the brass when reloading it. Also water quenching brass increases the annealing, the opposite to quenching steel.

Check your neck wall thickness before and after sizing down. I have found when necking up 6.5-284 brass to 284W that even though I have lubed well the process has introduced a wee bit of neck thickness variation. (If for hunting use probably not an issue.) Didn't matter though as I needed to neck turn for my tight chamber. Also if you neck turn your cases be frugal on how much you remove as this can also create extra brass movement in the chamber when fired and the ultimate need to anneal. Long time past I necked down 30-06 brass to 308W and I didn't bother annealing, only neck turned. I probably should have annealed though as I was necking the section of 06 brass that would have been the hardest in the case. Never experienced any problems in the life of the cases after that though. Re the sense of necking down brass to something that is commercially already available - heh that is the joy of reloading. Go for it, neck away.

When you come to do it do a normal re-size first with 308 die (assuming you have one) but with expander button removed. Put good chamfer on outside of neck, plenty of lube and size to 7mm. The effort required in the press is not great. Again you shouldn't have to anneal particularly only necking down one transition. Different if you were taking it through an intermediate calibre ie 2 sizing steps, which is what needs to be done with some creations. And I am not sure but necking up is probably more devastating for the crystalline structure than down, and up would definitely take the brass through its plastic limit. I have no proof of that gem though.

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Originally Posted by RimfireNZ

then air cool them (so they're not as brittle as water cooling), then bob's my uncle (after all the safety checks)?

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Other way round, quench them to make the brass soft. If it was just air cool then you would never need to do it as that would be the same as firing and letting the brass cool naturally.

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Originally Posted by Wirehunt

Other way round, quench them to make the brass soft. If it was just air cool then you would never need to do it as that would be the same as firing and letting the brass cool naturally.

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Been doing a bit of reading and yep, brass would be better annealed using water cooling (as zimmer pointed out this is the opposite to steel and what i was basing my previous post on). Of course still wouldn't be bothered using water as i wouldn't have the patience to wait for them to dry :)

But firing the case in your rifle is not the same as air cooling after annealing. Annealing you will get the neck of the case much hotter than just firing it in your rifle - well in all my rifles at least as i have never seen a case come out of one of my rifles glowing hot! Hot enough i didn't enjoy it going down the back of my shirt? Absolutely! But i haven't seen one glowing yet! :thumbsup:

What was the reason for necking down from 308 to 243?,jjust curious

here's where I ended up.
1 box of LAPUA 308 all run through a LEE f/l die with LEE lube in a LEE hand press.
Loaded,FED 210 43 grn V540 139 SST.


7mm08 SAAMI spec .3150

Loaded round LAPUA .3125

loaded 7mm08 FED .3105

SAAMI chamber spec neck at shoulder .3170 Neck at throat .3160

Fired neckdown case throat .3160

Make of it what you will:yarr:

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Originally Posted by Neckshot

What was the reason for necking down from 308 to 243?,jjust curious

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I had lots of 308 fed brass and no 243.

sweet