Despite the name, this collection covers more than case length. You'll find gauges that check sized brass, finished rounds, and your rifle's chamber, from Lyman, RCBS, Hornady, and Frankford Arsenal, in cartridges from 9mm and .45 ACP to .223, .308, 6.5 Creedmoor, and 338 Lapua Magnum.
Which gauge does what
- Case length and headspace gauges. Lyman's gauges show at a glance whether sized brass is within length and headspace limits, so you know when it's time to trim.
- Ammo checkers and cartridge gauges. Lyman makes these cut to chamber dimensions. Drop a loaded round in to confirm it will chamber, which is especially handy for AR and pistol ammunition.
- Chamber case length gauges. RCBS makes these for pistol cartridges such as 9mm and .45 ACP to check case length and fit together.
- Headspace and seating micrometers. RCBS makes micrometer-style gauges that measure shoulder position and bullet seating in thousandths, so you can size bottleneck brass to your own chamber.
- Overall length gauges. Gauges from Hornady and Frankford Arsenal use a modified case to find the distance to your rifling as a starting point for seating depth.
Gauge or caliper?
A gauge gives you a fast pass or fail for one cartridge, while calipers measure any dimension on any case. Most reloaders use both: calipers for exact numbers and a gauge for quick checks across a whole batch. You'll find calipers and other tools in measuring devices.
When the gauge says trim
Brass stretches a little with each firing. When cases start running long, trim them back with a tool from case trimmers and prep centers, then check them again. Clean brass gives truer readings, so a pass through one of our case tumblers first helps too.
Finding your cartridge
Every gauge here is cartridge-specific, so search this page by caliber to find the one that matches your rifle or pistol. Gauges for AR cartridges like .223, 300 Blackout, and 6.5 Grendel are especially popular, because a quick drop-in check catches rounds that might not feed or chamber in a gas gun. If you're not sure which type you need, start with a case length gauge for brass prep and an ammo checker for finished rounds.
