Action Wrench
A tool that clamps a rifle's action securely so a barrel can be torqued on or off without marring or twisting the receiver.
An action wrench grips the receiver firmly enough to resist the considerable torque needed to thread a barrel on or break one loose. Some designs are clamshell clamps machined to a specific action profile, while others use an insert or a rod that engages the bolt raceway, but all of them share one purpose: hold the action rock steady while force is applied at the barrel. Without one, the only way to grip the action is in a way that risks bending or scratching it.
The action wrench is the natural partner to a barrel vise, which clamps the barrel from the other end. Together they let a smith torque the joint to a precise value, which is essential gunsmithing for swapping a barrel or fitting a shouldered prefit barrel at home or on the bench.