Hi Folks. Never tried this yet. When my local shop is out of 7mm-08 brass.
What would be the easiest size brass to convert to 7mm-08.
They always seem to have 243,270 308 a plenty : I use Lee equipment.Thank you,jc

I have necked up .243 and necked down .308. Of the two, I prefer to neck up .243 brass. I would not neck up .243 brass if I had a .243 in the house.
My first 7-08 was when it was still a wildcat and, with mine, if I necked .308 brass down, I had to neck turn the brass to fit my chamber; If I necked .243 brass up, I didn't have to. This probably would not be a problem if you have a standardized 7-08 rifle.

Neck up .243 would be the fastest way. Necking down .308 may require the necks to be turned.
LEE uses a nice tapered decapping pin, so lubing the inside of the .243 and slowly enlarging to 7mm should not be a real problem.
If your worried about neck splits,anneal the cases first.

An alternate opinion from an old guy who has reformed quite a few cartridges over the last 35 or so years; if you have a stsndard SAAMI chamber, neck DOWN anytime you have the option.

Necking down will certainly thicken necks somewhat but your change will only make them about 1 thou thicker. Factory necks for most cartridges usually run close to 13 thou so your finished .308 to 7-08 necks would likely be quite close to 14 thou thick and standard chambers are very unlikley to notice such a small change. In fact, it won't hurt accuracy and may actually help a little because the cases wouldn't be quite as loose in the chamber while stretching up makes an already poor fit worse.

To KNOW, check a fired case neck and a loaded round with a micrometer. If your fired cases are at least two thou larger than loaded you'll do fine necking down. And nothing could be easier; lube the .308 cases, push them in a 7-08 FL sizer and you're done. (A fired neck is typically about one thou smaller in diameter than the chamber it was fired in.)

wasbeeman and Rapidrob. Thank you for that.I'll get busy and try my hand tommorow.
Jim C. Its quite a new Sako rifle I have. Will check out the case dia. Other friends have said it like you with regard to fls and possible neck turning. Was hoping to avoid that. Will keep you all posted how I get on.jc

Find some LC NM brass in 7.62 (easy to spot as it has a shallow cannelure above the web.
Neck it to 7mm08 and you'll have the best brass there is (except perhaps federal GMM 308.)
Also works just fine in 260 Rem, 338 Fed and 358 WRA.

Never turned a neck in any factory chamber.

I agree with JimC that necking down is usually more satisfactory than necking up. Factory chambers, even Sakos (and I own virtually nothing but Sakos), typically have rather generous neck dimensions. The slight thickening of the neck walls due to necking down makes for a slightly better fit, very rarely requiring any neck thinning when going from .308 to .284.

When necking up, on the other hand, the neck walls not only grow thinner, they also tend to do so a bit unevenly, leaving the necks with thin spots, which in turn tend to make your finished cartridges a tad out of concentricity. This is hardly "fatal" to a hunting rifle's accuracy, but still, the neck-down is more desirable.

As far as brass stretching, or growing longer, when necking down, yes, it tends to do so more than when necking-up. But any lot of brass needs to be trimmed to a uniform length anyway once it is reformed, so what's the issue?

By the way, I have necked down .308 cases all the way to .243. With commercial brass I've never needed to thin the neck walls; only with some military brass in some chambers has thinning been necessary.

Thanks once again folks,some stuff to try out. Everything Ive learned about reloading comes from AR along with some reading of the manuals. About to show my ignorance here.if you use the 243 to neck up, why not the 270.jc

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About to show my ignorance here.if you use the 243 to neck up, why not the 270.jc

It will work fine, sorta. You would be necking down because case body will necome new neck and it would be much too thick so neck turning would be demanded.

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Originally posted by Jim C. <><:

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About to show my ignorance here.if you use the 243 to neck up, why not the 270.jc

It will work fine, sorta. You would be necking down because case body will necome new neck and it would be much too thick so neck turning would be demanded.

Thanks Jim. Life in reloading is not as straight as the die. Dont think I,ll go there. jc

Don't want to get in a pissing contest with a couple of experts so just try it both ways and do which one pleases you.
Someone please explain why it is best to neck down? If the necks are uneven before you resize, they'll be uneven after you resize so that's not a valid argument.

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If the necks are uneven before you resize, they'll be uneven after you resize so that's not a valid argument.

Would you disagree that a neck that's already a loose fit in the chamber will surely be looser if it's stretched larger/thinner?

The difference in finished concentricity of a sized neck will obviously vary towards the thin/soft side even if we're not changing caliber. But the only thing "aligning' an expander is hope while pushing the case into a sizer die does derive some measure of support from the die it's going into. I prefer a little help from the die rather than relying on hope. YMMV. ??

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Originally posted by wasbeeman:
Someone please explain why it is best to neck down? If the necks are uneven before you resize, they'll be uneven after you resize so that's not a valid argument.

Okay, I'll 'splain it in more detail:

No one said that the necks were "uneven" (of differing thickness around the circumference) before resizing. In fact, we may assume for purposes of discussion that they are perfectly even.

When stretching the neck outward as in necking-up, there is a tendency for some areas of the neck wall to stretch more than others (possibly due to the uneven alignment of the expander ball as it enters the neck as JimC alludes to in his post.) This uneven stretching can result in thinner spots in the neck walls, which are necessarily being thinned generally by the necking-up process.

Necking down, on the other hand, tends to push the brass together (and extrude it longitudinally, which is why necked-down cases grow a bit longer) which typically results in more uniform neck walls, as well as thicker neck walls which also typically fit the chamber better.

If necked-down brass has neck walls that are too thick, they can be thinned. Necked-up cases will almost certainly have neck walls which are too thin, but there is nothing you can do about that. Thin neck walls (especially those with even thinner spots) will obviously split more quickly, all things being equal. Less than optimally thick neck walls may also fail to provide adequate bullet tension.

To further illustrate: Think in terms of the .264 Winchester, .338 Winchester, and .458 Winchester, all of which share the same basic case. How satisfactory would you think that necking .264 Winchester brass up to either of the larger calibers would be? Yep, the neck area would split long before you got that .338 expander into the .264 neck, even if you expanded with a set of tapered expanders in multiple steps. And the reason that it would split is that there would develop thin spots in the neck walls, at one of which the neck would eventually have to split. Stretching it to .458 would be way beyond the capabilities of the brass. HOWEVER, going down from .338 or even .458 to .264 would, with the proper intermediate steps, be no problem (although you would undoubtedly need to thin the necks once you got there, as well as trim the OAL.)

For something like the 7mm-08 I would always recommend starting with good quality 7.62 Nato military brass. It has no caliber headstamp, it is not expensive and it is easy to find. I much prefer necking a case down.

The only time I neck up a case is when the brass is really cheap and the original headstamp is expensive or hard to find. For me that is the .358 Win which I make from US GI 7.62, 8X57 Mauser which I make from US GI .30-06 and 7.65 Mauser which I make from either .270 (I do not own a .270) or .30-06.

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Originally posted by Stonecreek:
I agree with JimC that necking down is usually more satisfactory than necking up. Factory chambers, even Sakos (and I own virtually nothing but Sakos), typically have rather generous neck dimensions. The slight thickening of the neck walls due to necking down makes for a slightly better fit, very rarely requiring any neck thinning when going from .308 to .284.

When necking up, on the other hand, the neck walls not only grow thinner, they also tend to do so a bit unevenly, leaving the necks with thin spots, which in turn tend to make your finished cartridges a tad out of concentricity. This is hardly "fatal" to a hunting rifle's accuracy, but still, the neck-down is more desirable.

As far as brass stretching, or growing longer, when necking down, yes, it tends to do so more than when necking-up. But any lot of brass needs to be trimmed to a uniform length anyway once it is reformed, so what's the issue?

By the way, I have necked down .308 cases all the way to .243. With commercial brass I've never needed to thin the neck walls; only with some military brass in some chambers has thinning been necessary.

Stonecreek, you and Jim C have really caught my interest here as I have never heard of this 'preference' to necking down rather than up. I have necked 308 down to 7mm-08 with no problems what so ever just because i had 308 brass on hand when acquiring my first 7mm-08 years ago.

In this last year I have acquired a 6.5-06 with some 30-06 cases necked down (no neck thinning required) and like the previous owner got great performance and groups when loading 140gr A-Max and Sierra bullets. Since going the route of necking up 25-06 brass I don't seem to have got the same accuracy in fact I have been starting to blame the scope or fouled barrel for this. In the mix I have got some later batch powder of the same number previously used but also thought this may have changed things too.
The barrel is a Douglas Supreme possibly custom chambered for necked down 30-06 brass

Your postings have got me thinking, get some 30-06 and neck down!!! I'm excited.

Yep, I've learned something to try if I ever have to make 260 Rem cases - I should be OK at present, I have 200 Lapua, so I'll be fine for a month or so.

Thanks Guys, More stuff learned and to try from the folks on AR. jc

It all sounds good....in theory. In actual hands on doing, when I got my first 7mm-.308 (that's what it said on the Douglas premium barrel) I had a good bunch of .243 brass. I expanded a bunch, gave them a suggested load of H4895 and seated a 140 Sierra bullet. The first 10 rounds to ever go down that barrel measured 7/8". (so much for "breaking in" a barrel) That was merely resized .243 brass, not fire formed nor neck turned nor anything nor with any actual work up. That was better than I "hoped". It got better after I got some of the brass fire formed and doctored on my powder charge a bit. I also used some milsup .308 brass. I had to neck turn it but could see no improvement in accuracy. Just an added chore.
And, as far as the neck being "looser", I'm not sure that would make a difference as the cartridge lies crooked in the chamber anyway. If you're talking about turning the necks to precisely fit the chamber as in bench rest, you're looking at a lot of work for a hunting rifle. Too often, folks want to take a single facet of bench rest and turn it into a doxology.

I have necked 30-30 down to 6mm and up to 358. I have had to turn the necks on the 30-30 6mm because they were too think for my minimum chamber. I have also taken .223 to 6mm without problems and used 308 to make 358win without problems. I have used commercial and military brass and I get a split case once in a great while when using older brass. I now anneal the brass before any forming just to be on the safe side.

You will quickly discover what your chamber and its neck will accept. If you have a minimum chamber you are likely to have to turn the necks. It's not a big deal and you only do it the first time.

As for thin necks you can solve the fit problem by only neck-sizing the 80 to 90% of its length - leaving the un-sized portion to help align the front of the cartridge.

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Originally posted by PaulS:

As for thin necks you can solve the fit problem by only neck-sizing the 80 to 90% of its length - leaving the un-sized portion to help align the front of the cartridge.

Works good doesn't it.

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Too often, folks want to take a single facet of bench rest and turn it into a doxology.

You cannot deny the laws of physics either.

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Originally posted by PaulS:
I have necked 30-30 down to 6mm and up to 358. I have had to turn the necks on the 30-30 6mm because they were too think for my minimum chamber. I have also taken .223 to 6mm without problems and used 308 to make 358win without problems. I have used commercial and military brass and I get a split case once in a great while when using older brass. I now anneal the brass before any forming just to be on the safe side.

You will quickly discover what your chamber and its neck will accept. If you have a minimum chamber you are likely to have to turn the necks. It's not a big deal and you only do it the first time.

As for thin necks you can solve the fit problem by only neck-sizing the 80 to 90% of its length - leaving the un-sized portion to help align the front of the cartridge.

Thanks Paul, My local shop had a bag of Lapua 243 brass so I,ll see if I can make it work.jc

"I have had to turn the necks on the 30-30 6mm because they were too think for my minimum chamber."

And the doxology point of a minimum chamber is ... maybe ...a tighter fit??

I necked up the lapua 260 Rems for my 7mm08 but it does have a custom tight neck chamber. They really shoot good.