Shotgun technical advice
Headspace is the space between the cartridge head and the breech face, when the gun is closed.
The gap should be no more than a few thousandths of an inch, otherwise you may suffer from excessive recoil, among other problems.
Headspace gauges can be used for checking.
They usually come in pairs – a ‘go’ gauge and a ‘no go’ gauge.
When they are inserted in the chamber, the gun should close over the ‘go’ gauge, but not over the ‘no go’.
The usual difference between the gauges is around 0.005 inches.
If the space is excessive, the usual solution is to re-joint the gun.
In fact, excessive headspace can be a symptom of worn jointing.