Paradox,
I don't think the actions are tested,they have already been proofed and the makers of ELs know from experience which actions are suitable for which cartridge.However, there are two different lines of answers in this thread.One is for insert barrels(einstecklauf-EL)and the other is sleeved barrels.Zimmerman and Henneberger, as well as many others,can also do this work.Avaliable calibers are pretty much dependent on the particular action.Once the barrels are sleeved, they have to undergo full proof testing.
Mike
