• Primary Extraction: What is it?

    It seems a number of people out there don't seem to know what primary extraction is or what it does. Hopefully this quick FAQ and the accompanying video's will resolve that.

    Primary extraction is the initial phase of extracting a fired cartridge from the chamber of the rifle by mechanical means; typically in the form of a ram or cam built into the action and/or bolt assembly. As you rotate the bolt, two cams or ramps interact and mechanically draw the bolt (and cartridge) rearward a short distance.

    On a 110-series rifle, one ramp is built into the bolt handle and the corresponding ramp is built into the rear baffle. As the bolt is lifted and the two ramps meet, the bolt body slides rearward a short distance bringing with it the cartridge. The rear baffle effectively remains stationary as it's front surface is against the rear face of the action. (this is why the grooves that the rear baffle detent balls ride in are there - to allow the bolt to travel).

    Here's a quick video showing the Savage 110's primary extraction in action. Note how when the ramps meet they push the bolt-body rearward.



    On the Savage Axis rifles, one ramp is built into the bolt handle and the corresponding ramp is built into the action. It's effectively a simplified version of the 110-series setup which eliminates the rear baffle.

    Here's a quick video showing the Savage Axis' primary extraction in action. Note how the whole bolt assembly moves rearward as you rotate the bolt the last 10-15 degrees.



    Now that we know what Primary Extraction is we can explain why it is necessary on a high-power rifle. Most centerfire rifle cartridges produce anywhere from 50 to 65kpsi when fired. All that pressure expands the case into the walls of the chamber which makes for an extremely strong friction fit. The role of primary extraction is to use mechanical leverage to overcome that friction and allow the case to be extracted from the chamber.

    Generally speaking, the larger the cartridge the greater the need for primary extraction. This is due to the increased surface area of the case, or the amount of contact surface between the case and the chamber. The greater the area of contact, the more mechanical leverage you will need to overcome the friction.

    As one would expect, if there's a tolerance issue with the primary extraction ramps it will result in extraction issues or "stuck bolts". This is particularly true with high pressure cartridges with fatter cases like the WSM family of cartridges or the .338 Lapua Mag.

    DISCLAIMER:
    The information contained in this article and/or the attached video are for educational purposes only. Should you choose to use this information to alter or modify your firearm you do so of your own accord. In doing so you accept full responsibility for any adverse affects, damages, injuries and/or death that may occur as a result.





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