Sure, the key is to use quality components from reliable companies and get a good smith (or again yourself if you are capable which money on this forum are) to build it. While certainly not limited to something like the following, this would be a rifle which would exemplify the traits I've stated ITT:
**Upper**
- Barrel: Proof Research 20in 6.5CM with +2 gas system $829. Or you can have your smith spin up any number of high quality blanks (Bartlien, Krieger, Rock Creek Cut, etc) and use a JP barrel extension, and of course match the bolt.
- Upper: 2a Armament Xanthos $325 (includes lower below). Obviously you'd thermalfit whichever barrel/extension you went with.
- Port Door: V7 lightweight $37.
- Handguard: 2a Armament Xanthos XRVC 15in $264. Or insert your favorite DPMS high handguard here, MI, Odinworks, etc.
- Gas Block: Superlative Arms .875 (or whatever you cut the barrel to, the linked barrel needs .875) clamp on AGB (or SLR if SA is out of stock) $90. Loctited, or set-screw dimple if you want to go that far.
- Bolt Carrier Group: JP High Pressure Enhanced Bolt assembly group $213 + JP Low Mass .308 carrier $267. Can probably find both on sale elsewhere for cheaper. Now this is key, since the bolt and barrel aren't matched (assuming buying linked barrel) the thing to do is to buy the bolt first, and send it in to whomever you get the barrel from to make sure it is matched to the chamber.
- Gas Tube: Comes with barrel. If not using a +2 then the V7 Inconel gas tubes for ~$60.
- Charging Handle: PRI Gas Buster $80, or a BCM if you prefer $50. Radian and Noveske also make nice ones in this price range, but I haven't tested them myself.
- Muzzle Device: Place holder is a V7 titanium 5/8x24 brake, but really whatever suppressor floats your boat. If I were buying today I'd get a Q Trash Panda (instead of my current Omega although the Omega is great).
**Lower**
- Lower Receiver: 2a Armament Xanthos $325 (included above).
- Small Parts: This is where you can save some money by just buying a CMMG or, Aero AR10./308 LPK without the trigger or grip for around $40. But if you want to go all out and save a bit more weight/add a bit more durability you can just get all the V7 titanium shit: V7 Takedown pins $35. V7 Bolt Catch $27. V7 Ambi Safety $59. V7 TI End plate+Castle Nut $59. V7 Buffer retainer $7. V7 TI Grip screw $7. V7 mag catch/release $46. Finished off with a few extra springs.
- Trigger: Hiperfire Eclipse $199, or insert your favorite trigger here.
- Buffer Tube: V7 2055 $79.
- Buffer Weight+Spring: JP SCS Gen 2 $130.
- Stock: Luth-AR Carbine Stock $115.
- Grip: I'm a huge fan of the Hogue 15 degree $17, but there are a ton of great ones out there like the BCM or similar grip $19 (personal preference part).
Total for just the rifle is between $2800-3300 depending on options chosen and it should weight a little under 7lbs. Just to restate what I've already had to say too many times, sending this off to ADCO, Compass Lake Engineering, Whoever Proof Research recommends work on their barrels, Craddock Precision, River's Bend Gun Co, MSTN rifles, and Patriot Valley Arms would net the desired result.
So please Primus, tell me why all of these high quality components from excellent companies put together by an expert smith fails to live up to my claims. Tell me how a JP bolt matched to a JP barrel extension with a JP SCS and an adjustable gas block is somehow going to be less reliable than a JP. Please tell my why Padom can make .75moa AR10s for $1000 at home, but we are all too dumb? Tell me why CLE uses the DPMS standard parts and turns out reliable hammers, but somehow couldn't do it with the above parts?
I prefer to build my own, and I do not hesitate to spend as much on a home build as a high end rifle would cost.
That being said, a large shop can do things a home builder can't. For example, you mention the thermal fit. If for whatever reason the fit between an upper and barrel extension is loose, the large shop can always mix and match parts to get a better fit. A larger extension, or possibly even go machine an extension to that looser upper. A home builder in that scenario is SOL. This happened to me when I ordered a MATEN with the hopes of a tight fit. Unfortunately mine is on the looser side of things and there's nothing I can do about it except bed the extension.
I still prefer to build my own, but a manufacturer has more capabilities than a home builder.