Thread: necking up 243 to 7mm08

Is there any tricks to caseforming 7mm08 out of winchester 243 brass

I have a ton of it and need some 7mm08 cases for a new barrel thats on the way, I stopped in to my local gunshop and he told me its been out of stock and on back order for 18months

so plan B is to do a bit of case forming of maybe 40 rounds but I had a primer blow out and a face full of gas and a hell of a fright resizing 270win to 280rem
so I thought id ask here first this time

Isn't the shoulder moved forward on the 280rem specifically to stop it going into a 270win? That'd be asking for all kinds of problems when converting 270 brass to 280rem unless you created a false shoulder.

You won't have that problem converting 243 to 7mm08 - it should just be a straight neck up. Especially with Winchester brass because the shoulder material isn't really any thicker than the neck.

It would be nicer on the brass to use an intermediate 6.5 expander mandrel before the 7. Anneal it beforehand to be extra nice.

I might have few 7 08 cases you can have I think they are shiny federal nickel ones. I got given them as once fired I was going to take them down to 6.5
I will have a look tomorrow if you want them.

i have a spare 40 hornady once fired you can have,or a mixture of federal and winchester pay postage and they are yours

Iv had a very generous offer of 7mm08 Hornady cases for 223 cases which with 40 odd puts me on the path to gather more of them if I can, realistically 40 shots will probably do me for at least a year at current shooting rates haha


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Originally Posted by Hbwanderer

i have a spare 40 hornady once fired you can have,or a mixture of federal and winchester pay postage and they are yours

That would be awesome mate I’ll pm you


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Originally Posted by Pommy

Isn't the shoulder moved forward on the 280rem specifically to stop it going into a 270win? That'd be asking for all kinds of problems when converting 270 brass to 280rem unless you created a false shoulder.

You won't have that problem converting 243 to 7mm08 - it should just be a straight neck up. Especially with Winchester brass because the shoulder material isn't really any thicker than the neck.

What I can tell you is if you don’t size them to 30 cal then back down to 7mm approximately 3 of 10 blow primers and make you seriously reconsider how smart you thought you were beforehand.
Hard lesson but thankfully no injuries and just a bit of gas in the face


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I have necked up a couple of hundred .243 win cases to 7mm08 without any drama Remington Winchester Horandy all with one pass through a Redding FL die
it does have a nice tapered expander button which helps.

Better to neck down .308 brass if you have it, shoulder taper on the .243 sometimes means brass is weak in this area.

I neck up winchester 243 brass for my 260 Remington

Originally Posted by Bill999

What I can tell you is if you don’t size them to 30 cal then back down to 7mm approximately 3 of 10 blow primers and make you seriously reconsider how smart you thought you were beforehand.
Hard lesson but thankfully no injuries and just a bit of gas in the face


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Probably excessive headspace in action due to the steeper shoulder. Necking it straight to the required size isn't placing the shoulder in the right spot for correct headspacing so the head of the case isn't supported. That's why the step up to .308 or 7.62 is important, as when it's necked back down to 7mm it leaves a 'false neck' or a donut ring in the right place for headspacing. With that much shaking the neck size all about, annealing would be important I'd think. Especially on the first firing when the shoulder blows out to the chamber size.

Otherwise, it would be easier taking .308 cases straight to 7mm but it is safer to neck brass up as the wider pill dimension usually prevents chambering. I've had one .308 that swallowed a 7mm08 - wasn't very successful and the grouping sucked but I'm lead to believe that you shouldn't actually be able to do that?

Originally Posted by No.3

Probably excessive headspace in action due to the steeper shoulder. Necking it straight to the required size isn't placing the shoulder in the right spot for correct headspacing so the head of the case isn't supported. That's why the step up to .308 or 7.62 is important, as when it's necked back down to 7mm it leaves a 'false neck' or a donut ring in the right place for headspacing. With that much shaking the neck size all about, annealing would be important I'd think. Especially on the first firing when the shoulder blows out to the chamber size.

Otherwise, it would be easier taking .308 cases straight to 7mm but it is safer to neck brass up as the wider pill dimension usually prevents chambering. I've had one .308 that swallowed a 7mm08 - wasn't very successful and the grouping sucked but I'm lead to believe that you shouldn't actually be able to do that?

yea man all that would help, I just like mentioning it often incase someone reads it before falling in the same trap
I discarded all my 30-06/270 and went with 280rem hornady brass. I was just being a tight wad and it came back to bite me

I hadnt seen a whisper about it before it happened so it really caught me off guard

Put plenty of hinu inside case neck and on outside of case. I use imperial wax. Straight through 7 08 die and boom!

Originally Posted by Ginga

Put plenty of hinu inside case neck and on outside of case. I use imperial wax. Straight through 7 08 die and boom!

ill keep it in mind mate, Iv been generously set up with some 7mm08 cases now so that should stop any silly whoops moments with either rifle