Chamfered Primer Flash Holes

In the modern realm of rifle shooting there would appear little remaining room for progress in the area of research and development… but we must keep on trying. Here’s how an internally chamfered primer flash hole affects shooting performance.

by Norman E. Johnson

In “.224 Valkyrie Precision Problems” (August 2019) author Joe Carlos discusses the titular cartridge in detail. This prompted me to expound on the effects of the inner chamfered or beveled primer flash hole. In the text he mentioned he had not personally conducted any testing related to flash hole tools. He further stated that Sinclair International makes a tool that inserts through the case neck to chamfer the inside of the flash hole. Precision shooters claim this creates a more even powder ignition. Some claim this tool results in more consistent velocities. All this strongly suggests further investigation in this area may be helpful to the shooter.

Perhaps my more than 60 years of experience working with all aspects of the modern day cartridge may shed some light on this not-oft-discussed subject as well. While I have been unable to solicit any reliable outside information on the subject of inner primer hole chamfering, the following research is largely that which I have previously worked with over an extended period of time, and now, more recently.

Primer Function

The primer consists of a …

Read more in the August 2020 issue.

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