Quote Originally Posted by trackmagic View Post
I have a few projects coming up that will require me to remove and install barrels so I have been looking up information on head space gauges. I think I understand most of it, but I still had a few questions. Please correct me if anything I say below is not correct:

Are No-Go Gauges the same as field gauges?

Are No-Go Gauges the most important?
It seems like most people who post say that excessive head space is the most dangerous. What is the point of the go gauge? Should I get them both?

What is the proper way to read the Gauges?
From what I have read a no-go gauge should prevent the bolt from locking up, but a go gauge should allow it to lock up.

Do I need a 5.56-marked gauge?
Several people on different threads have recomended this gauge:
http://www.brownells.com/gunsmith-to...-prod6646.aspx
It says 5.56 in the description, but it says .223 on the side. Should I be worried about it not being marked 5.56? This does not say it is a "go" gauge so I assume it is a field gauge.

Do I need to check headspace if I take apart a factory rifle?
One of my "projects" is going to be taking the barrel nut off my current gun to install a FF rail. The same barrel and bolt will go back together. Should I worry about headspace in this case?

Are there any headspace gauges that do not require removal of the extractor?
It seems like most people say this is required, but I was thinking maybe there was one somewhere that would not require me to remove this.
Here's my understanding to a few of your questions after talking with Forster gauges myself:
1. No-go gauge = close to bad...field gauge = bad
2. I would say a field gauge is most important, hence the name in the "field"
3. Measure by removing extractor assembly, you can leave ejector pin assembly intact
4. Gauges, to my understanding:
Gauge /.223 chamber / 5.56 chamber
.223 Go = .223 Go / 5.56 beyond Go
.223 No-go = .223 No-go / 5.56 Go
.223 Field = .223 Field / 5.56 No-go
5.56 Minimum = .223 Go / 5.56 Go
5.56 Maximum = .223 beyond Field / 5.56 Field
5. A bolt may lockup on a No-go gauge but is close to extreme tolerance, should only use factory ammo to my understanding...?
6. I purchased Forster gauges myself