I just bought a 358 win. . I was trying to find a use for the 243 brass I have since I don't own a 243win. .
Also to keep from buying 358 brass or resizing 308 brass and possibly getting the resized 308 brass mixed up since I do own two 308's. I took 5 cases and ran them through a .260rem. fl die using resizing wax. Then through a 7mm-08 fl die. cleaning, measuring and relubing before each bump up to the next size. Then I ran the 5 case through a .308win fl die. I trimmed each case to 2.008-2.013. I then loaded each case with fed 210 primers, 44.0gr of blc2, and 180gr barnes x bullets w/COAL at 2.80. I then fired each loaded bullet in the 358win. to fire form the cases to 358. I had one case to split in the neck. Each case grew in the neck area and looks rather thin. the dia. of the neck is larger than .388; more like .390 and a 358 bullet just falls right end. This may work but I don't think the case will last and it is alot of work. I can either resize .308 brass or just brake down and buy the right brass when I buy 358 dies.

Kinda reminds me of the young lady who gave birth to an 18 lb. baby. Just stretching a good thing too far roger

I have to agree with Bartsche on this occasion stretching a 243win neck that far just isn't something that is going to pay off for you.

Yeah, you only split one, but how many will split on subsequent reloadings and firings?

And you already have neck tension issues due to the thin necks and I don't think that's a sizing button issue.
the brass simply isn't thick enough for the neck of the
die to make the ID the right size.

For the cost of cases and the number of them you are REALLY likely to use why not just break down and buy 200-300 NEW cases... that's likely to be more than a lifetime supply...

AD

With all that working of the brass in opening up those necks, I'm not surprised that the neck split. i did a bit of that type neck opening when I made some .375 Taylor brass from 7MM Ren, mag. brass. it helps to anneal the brass about half way through and then again after the final sizing up of the neck.
Still, when I got my forst .358 Win. I bought out all 550 rounds of new brass this gentleman was selling at a gun show. For a while, i though I'd screwed up and bought way too many. Now that I have five rifles in .358 Win., I'm thinking I don't have enough.
While the brass holds up real well, i would go along with the suggestion to get 200 to 300 cases. You never know when when the bean counters at Winchester decide to quit making it altogether.
Paul B.

You guys summed up the way I was feeling after doing it. I mainly wanted to try it because I have never re-sized any brass for another caliber before. I ordered dies and 100rds of brass after starting this discussion Sunday night. Looks like I may need to order more soon. Especially with the way brass just keeps going up.

The annealing is almost an absolute neccessity. I use 7.62x51 Lake City brass. Check the primer pockets. Once through the 308 small base die to bring it down from the possible oversized chamber of the M60. Then into the 358 Winchester die, each time applying die wax. The necks get shorter slightly ,allowing some shots before trimming. After I shoot them in my chamber I trim all to the same length anyway. Then I check for brass flash inside the primer hole. Sounds like you have figured most of this out with experience. The factory brass is much easier. And they will last for a good time barring excess or max loads. Good luck. Packy