Upper Receiver????

[Klem]

Not to veer the thread off topic, but are folks saying that you have to have an upper that you need to thermal fit or otherwise glue and shim to have a secured barrel and accuracy? I'll hang up and listen.

I argue there is more to tight groups than thermal fit however it will certainly help. Help, because the interface between the barrel and scope is equivalent to being seamless, but also companies that concentrate on such tight tolerances tend to be quality manufacturers; focussed on quality, and not necessarily quantity.

Thermal fit is a more recent innovation in the AR industry. There are plenty of tight grouping guns without thermal fits. Mate an Olympic grade stainless barrel with a 7075 billet upper and you can almost guarantee sub MOA without any post-purchase fiddling or thermal.