The Lyman Rifle Case Length Headspace Gauge for .300 WSM (brand part no. 7990344) lets handloaders check a critical safety dimension after resizing this magnum cartridge. Insert the case into the gauge to confirm it doesn’t exceed the maximum or fall below the minimum allowable headspace, and the gauge will also flag a case that has grown past the maximum allowable length. Lyman recommends this check after every resizing on bottleneck rifle cases, and any case found with excessive headspace should be destroyed immediately rather than reloaded.

Key Specifications

• Chambered for .300 Winchester Short Magnum, checking both headspace and case length.
• Confirms a resized case does not exceed maximum allowable headspace.
• Confirms a resized case does not fall below the minimum allowable headspace.
• Also identifies cases that have grown past the maximum allowable case length.
• Removes the guesswork from a critical rifle reloading safety check.

Frequently Asked Questions

Why does headspace matter so much on a magnum cartridge? Excessive headspace on any bottleneck case, especially a higher-pressure magnum like .300 WSM, increases the risk of case failure; checking after every resizing catches the problem before it’s loaded.

What should I do if my case fails this gauge? Destroy it immediately rather than reload it, per Lyman’s safety guidance.

Buy the Lyman Rifle Case Length Headspace Gauge, .300 WSM

Keep your .300 WSM brass safe and consistent with this Lyman headspace check. Browse our full case prep tools selection, and our Lubbock, Texas gun shop ships fast.