I have a SP1 upper and want to change to an A2 putting my short barrel on it. Can I set the headspace myself or do I need a gunsmith?

"Setting" headspace would most likely be a gunsmith function, but merely checking it is all you should have to do.  A gunsmith could also do this for you quite easily, or get yourself some GO & NOGO gauges from [url]www.fulton-armory.com[/url] & do it yourself.  (They come w/ instructions.)

The barrel headspace is set at the factory when the barrel extension is installed.  Since you are using the old barrel on the new receiver, the headspace will not change.  The barrel headspace is determined by the barrel extension and bolt only. This can be checked with out the barrel being installed in the upper receiver. Also, the barrel nut tightens the barrel extension to the upper, which is tightened to the barrel, and does not change the headspace.


Note: Since your receiver may be a SP-1 and the new A-2 being a mil-spec upper, you may have to buy an adapter to allow the two to work, due to the different size pins/holes.