Bramble,
Very true, but I'm bitten by the wildcat bug at the moment! Factor in the gunsmithing costs of getting a non-RUM action to feed a 404Jeffery or opening a standard length Mauser derivative, add cost of dies compared to honeing out a set of Lee 375H&H, factor in cost of brass compared to 375H&H (unless you want to use 375RUM brass which works at half the cost of 404 brass!) and the 404Jeffery is up against the wall in everything other than nostalgia. Even the 400 H&H, how many will buy proper headstamped brass compared to just opening 375H&H brass?

Besides, I'd not be game to dishonour the 404Jeffery by placing it in a Rem700 action. If it (423/375) fails to deliver ... its also a very easy rechamber to a 404Jeffery, 425Express, even 10.75x68 if need be.
Cheers...
Con