Go /No-go Gauge
This is a set of Go/No-go gauges for the .308 Winchester. This set just happens
to also work for the .243 Win. and the .358 Win. They are designed to be used when installing rifle barrels. These gauges verify that chamber clearance
(headspace) is within an acceptable range, according to SAAMI specifications. A chamber must have a very slight "extra" clearance to ensure that all makes of ammunition will fit.
It's best to remove the ejector on most rifles before using these gauges. This helps you "feel" the action close on each of the gauges. The Go gauge should fit in
your chamber, and the No-Go gauge should not fit. These gauges help verify that ANY factory load will fit in your chamber, and be safe to fire. This just means the chamber
clearance is "safe", although not necessarily a perfect fit for any particular ammo.
When reloading, it is important to always bump the shoulder of your cases back .001" - .002" to ensure a reliable fit in your
chamber. No accuracy is ever gained by crushing a cartridge into your chamber. This affects concentric alignment in a negative way, and it can wear the locking lugs
on your bolt. Keep in mind that most necked cases are tapered, and your handloads should NEVER press tight against the chamber wall.
Not all chamber reamers are perfect; and as they begin to wear out, they will cut chambers to a smaller diameter. A set of these Go /No-go gauges alone
can detect ONLY the depth of cut, not the work from a defective or worn chamber reamer. This is because this type of headspace gauge must be able to detetermine approximate
shoulder length on most rifle chambers.
Benchrest chambers are always tighter at the neck, and most of them require handloaders to reduce brass thickness at the neck. This is called
neck turning. I've seen a few poorly cut "custom" chambers that were actually a bit too tight (diameter) at the body. These chambers checked out perfectly fine with Go /No-go
gauges, but they had "excessively" tight body diameter. Some loads would actually jam tight against the chamber wall and fail to chamber any loads reliably.
Case width problems are commonly overlooked, and handloaders often find that belted magnum
calibers seem to have the most problems when chambering handloads. However, that's caused by the limited ability of conventional resizing dies when handloading belted cases.
Just keep in mind that most rifle Go /No-go gauges are ONLY designed to detect headspace (length) problems, and remember that "case width" is also an important