Do you really need to headspace check the bolt if you get a new barrel? Some say yes, others laugh at the notion. Can anyone clarify? I personally have been under the notion that as long as the bolt and extentions are "in spec" it was just a drop in and forget about it scenario.

You are correct.

The AR15 rifle has the ability to mix & match, 65% of the upper sellers on this very board choose to sell their uppers and hold onto the bolt/bolt carrier/charging handle of the upper for sale.

That said there are also those that buy new uppers and keep the b/bc/ch with the upper for as long as it is owned by them, (I'm one) and never swap old bolts w/ new uppers.

I have new replacement bolts should one of mine gets damaged or fails, and have no problems whatsoever using a new bolt in an old upper (where the orig has failed).

I have headspace gauges and use them on occassion, (most for folks mixing and matchin), so YMMV, but technically you can play musical bolts all day long with no worries.

Mike

98% of the time, it's perfectly within spec....closer to 100% if you stick with good components.

However, it's possible to have bad headspace. I just built an upper that was short on headspace, and this was with 5 different bolts. It couldn't be reamed because it's chrome lined so I had to mill-back the bolt face to get it in spec.