flutch wrote:Yeah righto lads, wonder how I would go sizing down 223 brass for the job
Yes it's easily doable but the cases will be a little short which will result in accelerated throat wear. Not too desirable in a caliber with a reputation for being a 'barrel burner'. A better case for reforming is a 222 Magnum but these days they seem rarer than 17 Rem.
In either case you will very carefully need to anneal the neck only and not the shoulder as otherwise you will lose a lot of cases with collapsed shoulders. The 223 case will be slightly trickier to form.
I use BM2 in mine but experience cratering well before reaching published maximum loads. I suspect I might do better with 2208.
17 Rem also has a reputation for being finicky to load to safe pressures.
I have given up chasing every last skerrick of velocity. Performance with the lesser loads is perfectly acceptable to the extent I have never bothered to chrongraph these loads.