I'm pretty much in agreement with Tirod on this. NORMALLY, headspace must be checked and adjusted. For non-AR type rifles, most barrels are sold short-chambered for just this purpose - the chamber must be finished-reamed and headspace verified after final assembly. You better know what you're doing.
But in this case the following apply also:
The Upper and Barrel were assembled at Anderson Mfg, and purchased from Brownell's. The likelihood of HS being not set correctly is minuscule. Likewise the bolt is from Brownells, and they DO NOT make a habit of selling out-of-spec parts.
I have now shot the rifle, very accurate, smooth cycling, and so far reliable. Brass looks fine. (I did shoot the first 5 rds. with protection, then examined the cases carefully). The only 'gunsmithing' I did on this rifle was to use a diamond stick to break sharp edges and a couple small tool marks on the BCG.
Regarding Brownell's, for those who don't know them. For gunsmithing tools and parts, it's true they are somewhat expensive. But imo they are well worth it.
For the 30 plus years I've dealt with them they've shown they actually care about the business they are in (guns and gunsmithing), high quality, and their customers. I've had reason to see this many many times over the past 30 years.
Their guarantee is absolutely unmatched. They will replace or refund anything they sell for free. No questions asked. I've used it several times in the past and they have never cared if part/tool was unused or if you've used it or installed it.
- I returned a special 1911 file once after using it 3 years, it dulled before it should have. It wasn't cheap. Replaced immediately free.
- I also once returned a 1911 hammer that broke (a premium hammer) that I had modified and used for a year. I told them I'd worked on it, they didn't care. Replaced for free.
- Returned an unused Kart NM barrel I ran across after 5 years, as soon as they could figure out what I paid for it, immediate refund.
I have no interest in Brownell's except as a very very happy customer. If I need a part or tool I need to be safe and dependable, I use Brownell's.