On Thu, 2 Aug 2018 07:02:24 -0700 (PDT), Its Me
wrote:

On Wednesday, August 1, 2018 at 9:41:49 PM UTC-4, wrote:
On Wed, 1 Aug 2018 20:02:12 -0400, Keyser Soze wrote:

Hardest part was learning how to properly
headspace a barrel. Do it wrong and possible kaboom.

More like a failure to go into battery, causing a failure to fire or
failure to extract, causing a double feed jam.

He's talking about the AR-15 he "built", and there's really nothing to headspace on one. If the barrel and receiver are properly machined to spec, it has the proper headspace built into the design. When it becomes important is when you are fitting a more traditional barrel and receiver together, and are doing the machining yourself. Let's say you have a Mauser 98 action, and you're building a 30-06 with a Shaw barrel. Then you have to check and machine in the correct headspace, and even then it's not hard to do.

My only real experience with it is reassembling an M2.