Neck up/down question

[Scoutdog99]

In general, is it better to size up or to size down when converting brass? I have a surplus of 308 and 243 brass, but I’m short on 7mm-08 brass. I actually have 308 rifles, but nothing in 243 so my preference would be to convert the 243 brass to 7mm-08. Are there any significant pitfalls to necking the 243 brass up to 7mm-08?

I realize I can buy/swap/trade for the 7mm-08 brass, but actually just converting brass is just something I’m interested in doing (because I can). Additionally, I understand that cartridge conversions can result in neck turning, concentricity, and runout issues that may have to be dealt with.
This rifle (an inexpensive one my wife shoots) isn’t used for any type of match shooting, rather just general target and sport shooting at 100 yards or less.

Thanks

[M-Tecs]

From a pure accuracy stand point I have had best results from necking down and neck turning. My experience is limited on necking up but when I have done it my runout increases. For your application I don't believe you will notice the difference. Since you don't have a 243 using that brass limits confusion.

[country gent]

Necking up necks get thinner and may not fit as well. Necking down necks get thicker and may require neck turning or reaming to fit. Watch neck wall thickness and concentricity when reforming brass. Brass may get thicker on one side and not the other, watch for banana shaped cartridges. Annealing may be required before or after, while normal reloading may move brass .003-.005 each sizing reforming moves it much more in the one time. I have sized 308 down to 243 with good results, it did need to be neck turned ( why I did it so I could fit necks to chamber), and a annealing. Brass worked great. Take your time use a good case lube ( sizing force will be more) and measure to stay ahead of issues.

[avan47]

I have necked down 308 to 7mm-08. Actually it was 7.62x51 LC brass, so no worries about the headstamp. It was an easy conversion with no neck turning needed. Brass works great, and is accurate in my rifle. Never tried going up from 243.

[rda72927]

14 months ago, my stepson received a LH 7MM-08 Savage for Christmas. Could not find any brass for it. I had a bunch of 243 and used it. I would suggest to anneal the brass before up sizing the neck. I didn't lose one piece of brass that way, lost a couple in the first try without annealing. We are on our 3 or 4 reloading cycle with the 150 rounds I made and have had no problems. I chose to size up because I have never neck turned any brass and really didn't want to. If I remember correctly, my neck walls went from an .014 average to .012 average. I don't work the brass much, I use a Redding S die.