I have spent some considerable time evaluating the different custom actions that could be used for any cartridge that uses the 338 Lapua cartridge as its parent cartridge and would love it if some other members wouldn't mind adding their two cents on the following subject.
I do believe that a custom action with a thread diameter of 1-1/16" is insufficient for this cartridge (read a good article about this by Jim Borden of Borden Rifles has to say about this on his website under a comparison of the 300 RUM to the 338 Lapua). The concern arises from the larger bolt face diameter of the 338 Lapua case and the intent of some, including me, to use this cartridge in any of the Remington 700 clone actions out on the market now. There are several action manufacturers that make a repeater action (Remingtom 700 clones) with 1-1/8" thread diameter but keep the diameter of the action body to 1.350" (the same as the Rem 700 action). Some have a slightly larger body diameter, and one that comes to mind adds .050" to its diameter. My question is basically the following. If you make a wildcat off of a 338 lapua case, are you asking for trouble by going with the larger thread diameter of 1-1/8"? Do you need a larger diameter than this even?
Second question: If you can buy an action with a 1-1/8" thread diameter but it retains the same diameter as the Remington 700 action (1.350"), are you getting too thin on the action to sufficiently support a heavy barrel?
Chime in and make a good argument one way or the other....