Lyman Rifle Case Length Headspace Gauge .300 AAC Blackout. The best way to check this critical dimension is with a Lyman case length/headspace gauge. The reloader simply inserts the case into the gauge to insure that it does not exceed the maximum or fall below the minimum allowable headspace. In addition the gauge will identify a case which exceeds the maximum allowable case length. Caution: Any case found with excessive headspace should be destroyed immediately. Specifications for Lyman Rifle Case Length Headspace Gauge .300 AAC Blackout: Manufacturer: Lyman Caliber: .300 Winchester Magnum .300 AAC Blackout Condition: New Package Contents: Lyman Rifle Case Length Headspace Gauge .300 AAC Blackout The Lyman Rifle Case Length Headspace Gauge .300 AAC Blackout 7832338 is a quality addition to the Lyman lineup. For more great deals on Gunsmithing Equipment by Lyman please browse our Lyman Gunsmith and Reloading Equipment page. Lyman Rifle Case Length Headspace Gauge .300 AAC Blackout