I have had an argument for a few years. But think I am ready to build my own. And I have a question about upper parts.if you do not buy a complete upper and buy all the parts separate. Is there gunsmith work that needs to be done to match the bolt or upper to the barrel.

No there is not.

Only when trying to use a well used bolt in a new barrel, is it required to check headspace. If it fails, there isnt anything you can do besides getting a new bolt that passes.

There are no reall adjustments like that in the operating system.

On an AR15 everything just screws together or gets pinned in place. No welding or riveting or anything like that.

If you can color inside the lines you can assemble an AR15. It's just that easy.

Exactly that ^^^^^^^

No special matching is done.

Ok thanks everyone. This will be my first build. I have watched multiple videos and I have seen some checking headspace. But apparently I don't really need to as long as I use all new parts. I think I am going to attempt a .224 Valkyrie.

Ok thanks everyone. This will be my first build. I have watched multiple videos and I have seen some checking headspace. But apparently I don't really need to as long as I use all new parts. I think I am going to attempt a .224 Valkyrie.

Well, I know that you are getting a number of responses that lead you to that conclusion, but let me voice a contrary opinion.  I believe you should check the headspace, unless the you are getting assurance that the barrel and bolt have been matched and checked by the provider.  If you are getting the bolt and barrel from two different sources, you should check the headspace. I do that when I assemble my rifles and have found only once where I had excessive headspace.  It turned out that the brand new bolt was out of spec (and that bolt was purchased from one the most highly respected providers here on ARFCOM).  It is not likely that if I had shot the rifle with that excessive headspace that I would have blown my face off, but it is likely that I would have experienced anomalous function at some point.  That great provider quickly fixed the issue by sending me another bolt after a couple of weeks of sending my assembled upper to them (they paid for the return shipping, too).  It's up to you, but I will always encourage new builders to check your headspace.  In your case especially since you will be building for a relatively new cartridge .224V.

Ok l was planning on checking it anyway just to be certain that everything was good. Thanks for your input I have already priced some gauges. I think they are a little pricey. But I really don't know. That could be the normal price.they want $100 for a three gauge set. It just could be because it is such a new caliber. I know the barrels are not overly abundant. And they are a little higher than the 5.56
Thank you. Joe