Works, but not the best option - AIM Sports Inc AR Upper Receiver Vise Block

I've built a few AR's now and not all of my upper receivers would work in this vise block. It's only worked on my basic mil-spec uppers; it wont work on slick side uppers or side charging uppers and without an action rod to go with it, it's not wise to be putting a lot of torque on a barrel nut or muzzle device. There are better options out there, and yeah they cost more money, but your better off with something else. This will work in a pinch but you shouldn't rely on it by itself.