Best Way Or Tool To Check Headspace?

[Rocky Raab]

For Moose or anyone else...

Headspace is simply the "fit" between a properly dimensioned cartridge and a properly dimensioned chamber. If there is too much room in the chamber (or too small a cartridge)when the cartridge fires, the brass will be unable to expand enough to contain the pressure, and will rupture. Hot gas, burning powder and metal fragments fly out everywhere. The gun may be ruined - not to mention your handsome features.

So excessive headspace is very bad, indeed.

Too little headspace is bad too, but you can't chamber a cartridge so it's less dangerous.

Headspace is set by one of three things: the thickness of a cartridge rim or the distance to the top edge of the belt, or (on cartridges with neither rim nor belt) the distance from the base to a point about halfway up the slanting shoulder.

Obviously, the first two methods are pretty simple to measure and set in the gun. But rimless cartridges are the very booger for setting headspace because the measurements are so difficult and elusive (Halfway up the shoulder? Measured from where on the rounded transition from the case wall to where on the rounded transition to the neck? See?)

So comebody invented the headspace gauge. It's simply a carefully machined steel device that looks like a cartridge with no neck or bullet. It comes in two or three-piece sets. The one that's sized to be normal is called the "go" gauge. If you can insert it in the chamber and close the bolt all the way, you're "good to go". The next one is just barely too big to meet the agreed-on dimensions for that cartridge. If you can chamber that one, you have a bit too much headspace, and it's a "no go". Finally - for wartime expediency - there's a "field" gauge. It's grossly oversized. In the field, an armorer would pass any rifle that would not close on the field gauge, and reject any that would. (Hey, slightly excess headspace is dangerous, but this is war!)

Today, some sophisticated shooters don't settle for a pass-fail headspace test. They want to precisely adjust the size of their cartridges to exactly fit their gun's chamber. So you can buy tools like the Sinclair gauge, which allows you to calibrate your sizing die to create cartridges that match your gun's chamber.

Note that now we've done a 180-degree shift here: in the past, we used a gauge to fit the rifle to standardized cartridges. Reloaders are now adjusting their ammo to standardized rifle chambers. Understanding what we're trying to fit to what is critical in this discussion. Just say "headspace" and it's easy to be confused.

Which is just where we came into this, right?