The Hornady Lock-N-Load Rimfire Thickness Gauge (RF17) is a precision caliper attachment designed to measure and sort factory rimfire ammunition by rim thickness. Because rimfire cartridges rely on the rim dimension for headspace and uniform priming compound distribution, sorting factory batches into consistent rim-thickness groups reduces standard deviation in muzzle velocity and tightens target groupings. The tool mounts directly to the anvil blade of a standard 6-inch dial or digital caliper via a thumbscrew clamp, delivering a repeatable manual sorting method for benchtop reloading and preparation setups.

Key Features

• Direct Caliper Mounting: Secures firmly to standard 6-inch dial or digital calipers with a captive thumbscrew mechanism, replacing improvised measurement setups.
• Broad Calibre Compatibility: Supplied with interchangeable bushings configured to seat .17 HM2, .17 HMR, .22 Short, .22 Long, .22 Long Rifle, and .22 WMR factory rounds.
• Consistent Measurement Baseline: Isolates rim thickness variations to help shooters identify rounds with identical seating depth and priming distribution.
• Passive Mechanical Operation: Requires no internal electrical power or batteries, operating entirely via the host measurement tool.

Specifications

• Model Number: RF17
• Tool Type: Rimfire thickness gauge caliper attachment
• Mounting Interface: Thumbscrew clamp fitting standard 6-inch dial or digital caliper jaws
• Supported Calibres: .17 Hornady Mach 2 (.17 HM2), .17 Hornady Magnum Rimfire (.17 HMR), .22 Short, .22 Long, .22 Long Rifle (.22 LR), and .22 Winchester Magnum Rimfire (.22 WMR)
• Measurement Resolution: Determined by the host caliper (typically 0.001" / 0.025 mm on dial calipers or 0.0005" / 0.01 mm on digital calipers)
• Power Requirements: None (100% mechanical)
• Throughput Capacity: Single-round manual placement

Who is the Hornady Lock-N-Load Rimfire Thickness Gauge For 17-22 Calibers for?

• Competitive benchrest shooters — Requires sorting factory ammunition down to tolerances of 0.001" or 0.0005" using a host 6-inch caliper, allowing this rimfire ammunition rim thickness gauge to minimise velocity standard deviation across match strings.
• Smallbore target competitors — Relies on uniform headspace across standard .22 Long Rifle match rounds, using this rim thickness gauge to batch factory cartridges into matched rim-thickness subsets.
• Precision pest control hunters — Benefits from tightening downrange shot dispersion on small game by sorting .17 HMR or .22 WMR field rounds using the gauge's dedicated caliber-specific bushings.

Less suitable for: Shooters using .17 Winchester Super Magnum (.17 WSM) ammunition or centerfire rifle calibres; larger-diameter rimfire rounds require dedicated wide-body rimfire tools, while centerfire cases require dedicated headspace comparators and bullet comparator inserts.