Barrel install tool

[jurassic]

Looking at the reaction rod, How does that hold the receiver to knock the barrel into it.

I have had only one barrel that was so tight I could not push it in with my hands, but that one did require putting the barrel in the freezer and heating the receiver with a heat gun. It went in easily and came out just as easily putting heat to the receiver again when I changed my mind. Other than that, snug barrels usually only require putting the muzzle down on something padded on the floor and pushing the receiver down.