Quoted: I'm looking to get a headspace guage for some of my C&R rifles to guarantee that they are safe to shoot.
The choices are from Brownells are:
"Go" guage "No Go" guage "Field" guage
Which one would I need, and what is the difference ?
Thanks!
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For rimmed cartridges, headspace is measured by the thickness of the rim. For rimless, it's the distince between some point on the shoulder to the base of the cartridge. A .303 guage is a tiny little thing looking like the last 3/4 inch of a cartridge, where a 7.62*51 guage looks like a cartridge with the very tip missing.
The Go is the shortest, followed by the No Go, followed by the Field. In laymans terms, it's how far the bolt holds the cartridge into the chamber. If it holds it too far out, you can suffer from a ruptured case because the steel of the barrel is not 'containing' the cartridge properly. The brass of a cartridge is like a play dough viscosity sealant at those temps and pressures. The base can handle it temporarily, but the thin walled part demands support from the chamber. If it's not in there correctly, you can suffer from a blowout.
Your bolt should close on a GO guage. If not, the headspace is too small. Ergo, the chamber is too shallow and needs reaming, or the bolt is too long. Generally, this will be an obvious problem as the bolt will never close correctly. If it closes under pressure, the biggest danger is that during use it may not close fully, and may fire under a partially closed condition. Not good.
Your bolt shoud not fully close on a No Go guage. If it closes on the go, and not on the No Go, you're in excellent shape. You are in SAAMI spec.
Your bolt should not fully close on a Field guage. If it didn't on a No Go, it has no chance on a Field. Use a Field when it closes on a No Go to see how bad you are off spec. Basically, the distance between Field and No Go represents a buffer area where if you are shooting new brass, it can probably take the excessive stretching without a problem. However, the brass gets badly mangled in doing so, although this won't be apparent to you. If this brass is reloaded and shot in the same gun a second time, you may get a blown case.
Beyond the Field guage, your chances of a burst cartridge go up quickly.