Originally Posted By: mj36639You do not need an action block. All you need is a good vice. I use two half inch thick pieces of polyethylene taped over the jaws(Hardwood like oak will also do). I chuck it in the vice sideways so the picatinny rail and the bottom of the upper receiver are the surfaces in contact with the polyethylene. Don't over do it. For assembling AR's you should at minimum have an armorers wrench, torque wrenches in inch and foot lbs, and moly anti seize grease in addition to common tools.
If you don't have much gunsmithing experience then an action block might be the way to go. Mistakes are expensive.
Bought an action block for my first build but my LAR ops-4 upper did not fit in it. I did just as described above making sure that the vise was clamped on the very front of the upper because it looked like there was the most metal there and it was closest to the barrel. It seemed fine and I was able to put 40 foot pounds of torque on the barrel nut.
I cut a .5 inch thick plastic cutting board for the jaw pads. I would just be careful not to tighten the upper any more that snug.
