Mark 7 Primer Orientation Sensor

Priming is critical when loading your own ammunition. The Mark 7 Primer Orientation sensor catches issues as they happen. 


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About the Apex 10 

Jon Vlieger from Mark 7 continues our video series on the Mark 7 Apex 10. Previously we’ve covered the Autodrive, powder adjustments, priming adjustments, and caliber conversion

At a stopping point between a caliber conversion and maintenance session, we decided to walk through the installation of one of the most important Mark 7 sensors, the primer orientation sensor.


The primer orientation sensor can be installed on any Mark 7 press and detects priming issues immediately after they happen. This helps you save components and time! 

This sensor detects high, low, missing and upside down primers. It also notifies you if there is no case present or if the shell plate didn’t index. The sensor includes a probe that makes contact with the primer and modifies the height of a “see saw” inside the sensor based on the depth of or lack of primer. You can set the sensor height with a properly primed case so the optical sensor in the sensor cable sees the nipple sticking out of the fulcrum when the primer is properly seated. If the machine does not see the nipple, it will stop the machine.

Here’s our video showing the APEX 10 with Autodrive:


Installation is extremely simple. Remove your existing spacer block from your primer housing by way of the two 9/64” bolts from underneath.

(This applies whether you have an Apex, Revolution or Evolution). Install a large spring towards the front and a small spring towards the rear with a light coat of red and tacky grease. (The sensor comes with extra springs as they are easy to misplace.)

Install the sensor straight down on top of the probe and secure the two bolts underneath. 

Primer Orientation Sensor Probe
Fasten Primer Orientation Sensor

Set-Up and Testing 

There isn’t an out-of-the-box one size fits all setting. You set the primer orientation sensor for the primers and primer seating depth you are using. Flush to 8 thousandths below flush is SAAMI spec. To set the sensor height, loosen the two 3/32” screws so you can slide the sensor up and down. With a properly primed case indexed, move the sensor block until it is flush with the indicator pin, then lock it down.

John recommends testing all sensors in the go and no-go scenarios. He enabled the primer orientation sensor and hit run for one cycle.

There was no error message and a visual inspection of the case showed it met our standards. 

For a no-go test, we put an unprimed case in the station and left the sensor on. We received an error message and the machine stopped. 

I liken this sensor to a powder check. 

Get the Gear! 

The Primer Orientation Sensor is available from Mark 7 Reloading. 

Mark 7 Apex 10

Mark 7 Auto Drive for the APEX 10

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Gavin Gear

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