re: Another building an AR-15 thread

I'm pretty sure that if you buy a completed upper with the bolt carrier already installed they check the headspace. But you might want to verify that.

I watched a video where a guy used a spent 9mm shell, a socket (can't remember the size) and a clamp to remove the ejector in order to check headspace. In other words, you don't have to buy all those tools from Brownell's that they use in their videos. just search youtube and you can find some good how-to's that aren't as hard/expensive as you might think.