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Making 308 Win from 243 Win

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Making 308 Win from 243 Win

Old 01-24-2021, 08:51 AM
Giant Nontypical
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Default Making 308 Win from 243 Win

Got a question maybe someone can help with. 308 Brass is VERY difficult to find right now and my wife bought me a 308 for Christmas and I have never used the cartridge so I don't have components for it. But, I do have a couple of hundred rounds of once fired Remington 243 brass that my late father shot up. Since the 243 is pretty much based on the 308 Win case I'm thinking of trying to open the 243 brass up. I can find a lot of info on line from going down from 308 to 243 but not the reverse.

All the dies I use are RCBS and I have 6.5x55 and 7MM Mag. I'm thinking I can increase the case mouth of the 243 brass in stages. I plan on taking the expander out of the 6.5 dies and the 7mm dies and use them on 308 dies and go from 6mm to 6.5 mm to 7mm to 30 cal putting lots of lube on the case mouth and then trimming if needed and fireforming the brass. In my mind this should work. My questions are:

Has anyone else tried something like this or am I looking at wasting my time and possibly wasting a lot of good 243 brass?

Would I be better off trying to trade someone 243 brass for 308 brass straight across? I am a little hesitant on this because I know for a fact the 243 brass has only been fired once since they were the factory 80 gr load that my late father used on coyotes but I wouldn't know the status of the 308 brass.

Any advice or input is greatly appreciated.

Last edited by flags; 01-24-2021 at 08:52 AM. Reason: typo
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Old 01-24-2021, 08:56 AM
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you should not have any real issues if you anneal the necks first and lube the case necks well,
before resizing I make 338 win mag cases from 7mm rem mag, and 358 win from 308, all the time
I generally use a q-tip dipped in vasoline as a lube inside and out side the case neck just before resizing
just after annealing the cases


Last edited by hardcastonly; 01-24-2021 at 09:01 AM.
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Old 01-24-2021, 06:48 PM
Fork Horn
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for me doing anything like this I find that a few steps work better than making the jump in one move, I would suggest going up to 6.5, annealing then try to go that rest of the way, if you have problems with split necks then don't hesitate to go to 277 or 7mm before going to 308. I have taken 25 wssm and made 358 bfg from that so going to 25 cal to 358 is a bunch more that what you are trying to do. good luck
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Old 01-24-2021, 07:10 PM
Nontypical Buck
Join Date: Nov 2014
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not sure if possible here , but what about fire forming the cases
I've done in a bunch of wildcat calibers over the yrs using a primed case, some powder some corn meal and a cotton patch, just enough charge to form case!
I have a recipe with exact amounts of each, I can dig up is you want! been about 20 yrs since I did so!

it does some times split a neck or two, but overall,, just examine them afterwards really well!
and does require some bore cleaning after doing some! minus wasting powders and primers too, but back when I did so, things were much cheaper for me to get having my shop and all!

but it did make me a bunch of brass for me over the yrs ,back when I shot a lot of things that needed them made!

two links to maybe read



Last edited by mrbb; 01-24-2021 at 07:18 PM.
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Old 01-25-2021, 03:13 AM
Nontypical Buck
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Be prepared for the resulting 243 cases to have shorter necks than spec. I don't think you can go from 243 to 308 diameter without losing case neck length.
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Old 01-25-2021, 06:33 AM
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Cases end up short and youíll often find a doughnut at the bottom of the neck where you pulled brass which used to be shoulder into the neck, so youíll likely end up neck turning. (Which is a good idea anyway, since your case neck ends up thicker as you smash the material of a .306Ē ID neck into a .241Ē ID form). What youíre wanting to do can be and has been done, and a little extra elbow grease will get you there. But itís still a major pain in the butt which I honestly donít believe is worth pursuing, even in the midst of this buying panic.

Iíd personally be patient and buy .308win brass when you can find it, or try to find someone to trade for 308 win brass.

I couldnít be bothered to waste time fireforming necks only to open up 243win to 308win. We fireform to move case bodies and move shoulders, which are case forming actions which simply canít be done any other way. Simple neck up jobs like this should never be done by fireforming.

Last edited by Nomercy448; 01-25-2021 at 06:35 AM.
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Old 01-25-2021, 07:31 AM
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I see the link I posted for available 308 brass sold out since yesterday
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Old 01-25-2021, 04:46 PM
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I've made 35 whelen brass out of 30-06 without any trouble but 308 out of 243 may be a bit of a problem. You could be better served opening up 7-08 brass. I've made 7-08 and 243 brass from 308 but not vice versa.
If you want to dump that .243 brass at a reasonable price drop me a pm. I may be interested.
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Old 01-27-2021, 08:20 AM
Join Date: Aug 2013
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Don't know if this will be helpful...

As of Wednesday morning

Powder Valley Powder Valley - Shop Reloading Supplies and Ammunition (powdervalleyinc.com)

has Starline brass in 308 Match. The ad says "small primer" I am clueless as to whether "regular" 308 aka 7.62 x 51 is the same as 308 match. Even if they are the same and you don't have small primers on hand you are out of luck.

Starline 308 Match Brass (Small Primer) | Powder Valley (powdervalleyinc.com)

I recently bought a bag of shot from them for my first ever purchase and can say that their order processing is a little slow but they did deliver.
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Old 01-28-2021, 07:30 PM
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308 Match is Starlineís answer to Lapua Palma brass. Itís standard 308win brass, except with small primers instead of large.

I have selectively used Lapua Palma brass for nearly 20yrs for all of my 308win family cartridges when precision is on the line. Itís as good as it gets, and lasts nearly forever. The Starline version isnít ďLapua good,Ē but itís still decent brass.
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