Quote:
Originally Posted by apollo99
There is a tool that holds the upper in place, it is like a magazine that goes into a vise, than a star like protrusion goes into the barrel where the bolt fits in, that tool will properly hold the upper, and stabilize the barrel.
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I think you're on the right path, but your description isn't correct and could cause problems.
There are two specific clamping devices for an AR. The first goes in the mag well and gives the user a block to put in a vise. This only for working on the lower and should never be used when torquing on the barrel because it could bend/break/crack the lower receiver.
The second is an Upper Receiver AR-15 Action Vise Block Clamp and looks like this:
It is two parts. The one part goes into the receiver in place of the BCG and supports the upper receiver so it doesn't get crushed in the vise. The second part goes around the upper receiver and gives you a flat surface to clamp to. Assembled and in a vise the whole package looks like this:
If you plan on doing any work on the upper, this is a good tool to have. This one is about $20. It makes life a lot easier.