You are correct. The action wrench is used in conjunction with a barrel vise. One thing to be aware of is that manufacturers sometimes change thier designs / you don't know the quality of the wrench, I would use it only with the utmost care.
The one pictured can be had from Brownell's, looks like my Mauser Wrench, most if my wrenches are home made, on some Mausers and M1917 I have had to extend the handle 4 ft., love that sound, the secret? A very good barrel barrel vise.
