L.E Wilson 303 British Gauge

The L.E. Wilson Case Gauge is a simple one piece device that allows the measurement of headspace using fired brass as well as maximum case length which is used to decide if case trimming is necessary.  Very simple, but well thought out, the gauge was invented in 1935 to solve a problem a fellow shooter of Sam Wilson encountered while on the range.

Thoroughly clean the gauge.  Take a fired case from your rifle and de-prime it.  Insert the fired case into the gauge.  Using a micrometer or calipers, measure the distance the case head protrudes from the lower surface of the gauge (the higher surface represents maximum headspace). This distance is the amount your chamber is over minimum headspace.  Adjust your resizing die so that sized brass measures 0.002 inches less than this distance using the gauge.  If the distance is negative, your chamber is below minimum headspace.  You will probably need a depth micrometer to measure the negative distance but you may be able to get by with calipers.  Again adjust your resizing die so that sized brass measures 0.002 inches less than this distance.  By resizing cases to this dimension and no more, you are lengthening the life span of the cases while ensuring they will function in your rifle.

To determine if a case needs to be trimmed, insert the re-sized case into the gauge and look for any protrusion of the case neck.

Wilson case gauges are calibre specific and this one is made for the 303 British cartridge.