405's are listed as having a bullet weight between .411-.414, with a barrel dimeter in that same range. The 10,3x60R and 10,3x68 RWS are listed as .413.

Is this for all intensive purposes the same?

Lutz Moeller, RWS, Impala and Collani all make bullets for the 10.3 rifles.

Hornady, Barnes, GS all make bullets for the .405.

Am I just splitting hairs?

Having owned ,40 Newton, 400 Whelen, 400 Hawk, 411JDJ , 411KDF and still owning a 405 Win-

I surmise, This new cartridge and the 400 H&H will develop a small following.
Neither would I expect to develop a large or long lived market share.

But if you have to have one - you can make brass out of other calibers and bullets can be found or made.

The 40 cals have a permanent place in the hunting fields,
Even if not The favorites of many shooters.

Though the .405 WCF ammo was originally a 300 grain JSP, modern loading components allow the creation of useful loads with bullets from 210 grains on up through 400 grains.
Though my big game choice is still 300 grains, my DG loads use 400 grain bullets and have proven to be very effective.
This goes for my Miroku/Winchester 1895 .405 lever action and my Simmons .405 double rifle.