I have a new (for me) A2 that I want to change into an A3/A4.

I've never tried to do this, but was wondering how difficult it is to swap out upper receivers. Not barreled uppers, just the upper receiver. What tools are needed, and how much expertise is required?

If it is a job for an AR smith, anyone know a good one in PA?

Thanks in advnce for the help.

If you want to remove the barrel from the upper you need an action block and a barrel wrench (get one of the all in one wrenches), a pin punch to remove the gas tube retaining pin and a vise to hold the action block. Dont try to improvise or it could end in tears.Search this site for instructions on how to do it.
When yo refit the barrel to the flat top upper you need to aline the holes for replacement of the gas tube.Dont go crazy over tightening the barrel nut!

Thanks thebloke. I thought it would be fairly simple. Will do a search and get a good set of detailed directions before attempting this.

The action block (DON'T BUY BARREL VISE JAWS) from Bushmaster, DPMS, and others should have instructions included.