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.

I believe all u have to do is run it up a 308 full length die with a good amount of lube. Please have others confirm as I'm not sure.

However, I have some used 308 brass that I don't have any assigned use for. I can give u a bunch, if u pay shipping. They will vary in headstamp and times fired but I bieve they're still usable. Pm me if you're intersted.

The 243 is based on the 308 case, but with a slightly different case length. The 243 is 2.045" and the 308 is 2.015". This difference could cause the brass not to work in the 308. And necking up 243 Win fired brass will thin out the necks and they could easily split. My general rule is not to go more than about .030" difference when necking up or down. Going from 243 to 308 would be .065", which is about twice over my general limit.

Will the neck be very thin after that much stepping up?

I’ve got a pile of once fired 308, same as KR above, pm me your address and I’ll hook you up. After I find it. It’s in a backpack around here somewhere.

PMs sent to both KR and WP

Do not just run the 243 through a 308 die . First depending on what die you have the expander ball may not even fit , also there are special "expanding" expander balls for step ups . You idea of a step at a time is best and will save many cases from splitting . Use lots of lube in the necks . I expand Hornady .223 cases up to .357 and the neck dia reduces from .009 to .008 . So depending on your case , 243 to .308 should not be as bad . The 243 cases will get shorter when you expand them up to .308 , check and see if trimming is needed . Unlike people who are just guessing at this , I have wildcatted 1000's of cases into many different rounds .