Precision Primer Gauge Instructions

Precision Primer Gauge Instructions

Using the Precision Primer Gauge to measure primer pocket depth, seated primer depth, and unseated primer thickness is simple. The following Precision Primer Gauge Instructions walk you through the process.

Measuring primer pocket depth

Loosen the black nylon screw that secures the gauge body and remove the indicator.  Select the primer stem that corresponds to the diameter of primer pocket you wish to measure, either large or small. Notice that each primer stem is double ended; one end flat, and one end concave. For measuring primer pocket depth, insert the primer stem into the gauge body, concave end first. This is important due to the fact that pocket uniforming tools often do not cut a perfectly flat bottom and ensures that you will be measuring the depth of the pocket in the area where the feet of the primer anvil will touch. Now, slide the gauge body onto the indicator and tighten the nylon screw. To zero the indicator; turn it on, and select the appropriate zeroing block. Each zeroing block is double ended. The smaller having a .223 (.378”) head diameter and a .308 (.473”) head diameter. The larger having a Magnum (.532”) head diameter and a .338 Lapua (.585”) head diameter. Place the end of the zeroing block into the end of the gauge body so that it rests squarely on the corresponding step and press the zero button. The indicator is now zeroed. The zeroing block can be placed aside. Place an unprimed case into the end of the gauge body, so that the head rests squarely against the step and the depth of the pocket will be displayed on the digital indicator.

Measuring seated primer depth

Loosen the black nylon screw that secures the gauge body and remove the indicator.  Select the primer stem that corresponds to the diameter of primer you wish to measure, either large or small. Notice that each primer stem is double ended; one end flat, and one end concave. For measuring the depth of a seated primer, insert the primer stem into the gauge body, flat end first. The face of a primer cup is slightly convex. The use of the flat end of the stem will ensure your readings will be taken from the highest point of the primer. Follow the same procedure for zeroing the indicator as you would for measuring the primer pocket depth. Place a primed case into the end of the gauge body, so that the head rests squarely against the step and the depth of the primer, below the face of the head, will be displayed on the digital indicator.

Measuring unseated primer thickness

With the large primer stem installed in the gauge body, either large or small primer thickness can be measured. Start by zeroing the indicator with the .223 diameter zeroing block. Now, hold the gauge body upside down, so that the open end faces up, and the exposed end of the indicator stem is facing down. Draw back on the exposed end of the indicator stem and you will see the primer stem retract into the gauge body. Place the primer you wish to measure on the tip of the primer stem. Place the .223 diameter zeroing block squarely on its corresponding step and gently release the exposed end of the indicator stem. The tension of the indicator stem will “pinch” the primer between the zeroing block and the primer stem. The thickness of the primer being displayed on the digital indicator.

General use in practice

It is common practice to use a primer pocket depth uniforming tool on a lot of brass to ensure uniform depth. As an example, we’ll use .131” as a figure for the depth of the uniformed pocket for a large rifle primer. Measuring the thickness of a lot of primers may show that the height of your lot of primers vary from .127” to .129”. With this information and use of the Precision Primer Gauge, you can be sure that all the primer anvil legs will be making contact with the bottom of the pocket when seated to .004” below flush, with none being crushed more than .002”.