headspace a single shot

[maggot]

How exactly would you go about headspacing a new england single shot?
Could you use a depth micrometer and set it below flush?I am new to gunsmithing!

[Flint]

Headspacing is gaged with appropriate headspace gages.  You open the chamber and insert the gage as if it were a cartridge, it will either Go (the breech will close) or Not Go.  The type of gage depends on where the cartridge headspaces, either the shoulder of a bottleneck rimless, or the rim (Thickness) of a rimmed cartridge.

[John Traveler]

Flint is correct.  the best way to check headspace is to use headspace gages.

Even without headspace gages, you can do a creditable job of checking headspace.

1.  Cut shim stock discs of cartridge head diameter.  0.002", 0.003", etc.  I use old feeler gage leaves.

2.  Lay on head of chambered cartridge and attempt to close the action.  Add shims until action won't close.

If you have a depth micrometer, you can measure depth below flush as you add shims.

3.  Your total headspace is the thickness of the shim(s) plus the depth micrometer setting.

4.  Nominal maximum headspace is 0.005" or 0.006" clearance.  Anything above that is considered excessive.