Thread: First attempt at necking down 308 to 7mm08

Well guys I had a go at this and didn't have any luck.

I got a few bits of that 308 brass I've got, put a tiny bit of lube on them, and slowly pushed it into the pull length 7mm08 sizing die.

I couldn't close the bolt on my rifle with any of the necked down cases. I also noted the necked down cases are a little bit shorter than the length I normally trim too. Not being able to close the bolt is a little concerning though and I didn't want to force it obviously.


I measured the outside neck diameter of the cases:

Once fired, fully prepped 708 case:
Outer width: 7.81mm
Neck width: 0.31

Once fired, fully prepped 308 military case #1:
Outer width: 7.96mm
Neck width: 0.41

Once fired, fully prepped 308 military case #2:
Outer width: 7.99mm
Neck width: 0.44

Once fired, fully prepped 308 military case #3:
Outer width: 7.94mm
Neck width: 0.41

It's a bit weird the necked down cases are wider.

You can see the actual necks are visibly thicker on the necked down cases (to be expected I imagine... probably need to be reamed out from what I hear).


And you can see the shoulder isn't quite right (necked down case is on the left)





You can tell the third case is the 7mm08 one


Where am I going wrong chaps?

I suspect you need to adjust your die down to compensate for the extra force required to size down.
Give one the vivid treatment and try to chamber to see where its hitting. Could be neck but more likely shoulder or body

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Originally Posted by veitnamcam

I suspect you need to adjust your die down to compensate for the extra force required to size down.
Give one the vivid treatment and try to chamber to see where its hitting. Could be neck but more likely shoulder or body

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I agree.

Screw the die another half turn into the press and see what happens also. You may need to go further than half a turn too...

Really need to do the vivid test to check body. Military arms can have large chambers and may need a body or small base die to get it back in size. Or if lucky and carefull may get away with it with standard fl die .

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308 will always be shorter than 7-08. What brand is the brass? Lapua? As you neck down the brass has to go somewhere. In already thick walled brass its going to increase the neck wall thickness. You may need to outside turn the brass.
I too think your FL die is not stroking the brass far enough. Don't pussy around with it either, give it a good shove in the press but try to also be consistent. Use a decent lube too. I doubt in a factory chamber it will have a tight neck but you may need to outside neck turn.

Originally Posted by kiwijames

308 will always be shorter than 7-08. What brand is the brass? Lapua? As you neck down the brass has to go somewhere. In already thick walled brass its going to increase the neck wall thickness. You may need to outside turn the brass.
I too think your FL die is not stroking the brass far enough. Don't pussy around with it either, give it a good shove in the press but try to also be consistent. Use a decent lube too. I doubt in a factory chamber it will have a tight neck but you may need to outside neck turn.

It's Lake City stuff (military) that's been all prepped down to 308 specs by the guy I got it from. It's supposed to be "ready to load".

I have my die adjusted down far enough that my press touches it when it goes up. I don't think I can wind it anymore (the only adjustment on that die is the primer remover depth).

I'll have another tinker tonight and put a few more pics up.

Originally Posted by RimfireNZ

It's Lake City stuff (military) that's been all prepped down to 308 specs by the guy I got it from. It's supposed to be "ready to load".

I have my die adjusted down far enough that my press touches it when it goes up. I don't think I can wind it anymore (the only adjustment on that die is the primer remover depth).

I'll have another tinker tonight and put a few more pics up.

presses generally flex a little when you have a piece of brass in there being sized so winding down more so that it bottoms out earlier can still be justified

Originally Posted by RimfireNZ

It's Lake City stuff (military) that's been all prepped down to 308 specs by the guy I got it from. It's supposed to be "ready to load".

I have my die adjusted down far enough that my press touches it when it goes up. I don't think I can wind it anymore (the only adjustment on that die is the primer remover depth).

I'll have another tinker tonight and put a few more pics up.

Just wind the die down!! Dont touch the decapper if the primers are already being removed

yea like HH and Wildman have said you need to wind that die down to compensate for the 'press flex'.

AS an aside what causes that ring on the case second from left in the last photo? Never seen that before

Or just give me the .308 brass. I'll take it off your hands to save you the trouble.

Now looking at pics on pc instead of phone the shoulder looks like at least a mm longer than the 7/08 shell, wind die down.

Originally Posted by veitnamcam

Now looking at pics on pc instead of phone the shoulder looks like at least a mm longer than the 7/08 shell, wind die down.

agreed

I have Hornady headspace gauge attachments, allows you to actually size the brass shoulder the same as the real 7mm08 brass. Same as what VC says with the vivid marker, just a bit more scientific like.
Let me know if you want to to borrow them this weekend. I'm in St Heliers.

Originally Posted by dogmatix

I have Hornady headspace gauge attachments, allows you to actually size the brass shoulder the same as the real 7mm08 brass. Same as what VC says with the vivid marker, just a bit more scientific like.
Let me know if you want to to borrow them this weekend. I'm in St Heliers.

Thanks Dogmatix,
I'll give the vivid treatment a go and try winding my sizing die down a bit and if I'm not having any luck I'll have to get a bit more scientific like and I'll flick you a PM.

I imported Paora a Redding 7mm08 Body die from Sinclairs, we can always nab that off him and give your brass a going over to bump the shoulder back more.