This is a basic gauge that allows you to verify whether or not your ammo is within the tolerances of an 8.6 Blackout rifle chamber. Machined in-house from 303 stainless steel. The top surface represents the maximum headspace (1.325″ from the datum line) and the milled step represents the minimum headspace (1.318″ from the datum line).
When we began researching the 8.6 Blackout cartridge, we could not find any of these so we had to make our own using a PTG reamer (see image). I decided to offer this no-frills, basic go/no-go gauge for reloaders looking to check their ammo (or even factory ammo) for a reasonable price. With 8.6 Blackout in particular, it is critical to either use a gauge like this or to check your TIR (total indicated runout) using a dial indicator. This is because 8.6 bullets are so long, they can cause chambering problems that are not present with most other cartridge and rifle combinations. I recommend checking all ammo, even if loaded with virgin cases, as a modest amount of runout can cause issues.
If excessive runout is identified i.e the cartridge does not buttom out in this gauge:
- Ensure that the gauge has not powder or debris inside of it
- Use this gauge to check your new or resized brass prior to any additional steps
- Use this gauge to check your brass after each step of the loading process (excluding flaring)
The first step of your loading process that causes a failure is obviously the culprit- where you are introducing excess runout. One common cause is using a seating plug that is not optimal, or even suitable, for your bullet profile.
Checkout two of my favorite 8.6 Blackout resources: