AR headspace independent from the bolt?

[AZRedhawk44]

Looking at this product:

http://www.bravocompanyusa.com/BCM-16-Mid-Length-Upper-Receiver-Group-p/bcm-urg-mid-16.htm

The BCM Standard 16" Mid Length Upper Receiver Group


To my understanding, there's a paradox in their product description:

Made by Bravo Company MFG, Inc. (BCM®) These Barreled Upper Receiver Groups are designed for shooting professionals with the Mil-Spec features for the demands of their duty. They are fully assembled, headspaced, and test fired. These do not include bolt carrier groups or charging handles.

How can an upper receiver group be "headspaced" if it doesn't come with the bolt?

I'll admit to being predominantly an M1 and M14 shooter and rather new to the AR-15 scene... but the bolt contact surfaces are a major component of headspace, to my understanding.

Can anyone enlighten me?

[bedlamite]

They are assuming you use a bolt that is in spec, the headspace is set by the barrel extension when it's assembled.

[Monkeyleg]

A bottleneck cartridge headspaces on the case shoulder, so they've probably measured back from the shoulder portion of the chamber to where the bolt should be when it locks up.

I just said the same thing as Bedlamite, but worded it differently.

[brimic]

New barrel+new bolt= no worries.
Some places do headspace the barrel/barrel extension to a specific bolt, but those are custom match barrel jobs.