Can I build a 405 WCF on a Krag rifle action? Is that a possible thing?

The basic answer is Yes it can be done and it has been done. Here is a reference you may be able to exploit for some more solid information.

http://www.doublegunshop.com/f...mber=215394&page=all

Scroll about half way down to a post by mkbenenson date 20-02-2011.

You have probably seen the discussion above about converting the SMLE to .405 WCF.

Thank you!

My pleasure. That's why we're all here.

Dan Pederson did one for a customer of mine a couple of years ago. He rebored the barrel and did the action modifications to make it feed.