1:7" will also suffice very nicely.
The OP (RinB) did not state if he was buying a new rifle or putting on a new barrel, just asked what the best twist was for a 223 with 50 grain bullets.
In reality a 1-14" twist would be optimal, quite a few bolt action rifles come with 1-12" barrels some with 1-9". If shooting factory ammo you might not notice much of a difference but to suggest a 1:7" is flat out stupid, but that is what froggy is famous (or infamous)for.
