Thread: 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.

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.

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.

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.

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 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

Originally Posted by Cyclist

Probably ok but NOT always 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

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

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

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.

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.

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!

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!

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.

Originally Posted by Cyclist

Probably ok but NOT always 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

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