Ultimate Reloader Explains What Headspace Gauges Actually Measure

Headspace is one of those words that gets thrown around in gun shops until nobody's quite sure what it means anymore. In a video from Ultimate Reloader, host Cam sits down with Ray Gross of Manson Precision Reamers to actually define it, and to show what go, no-go and field gauges can and can't tell you about a rifle's chamber.

Snapshot

Cam and Ray Gross break headspace down to its basics: the clearance between a chamber's reference surface and the matching datum point on a cartridge. They walk through SAAMI's minimum-to-maximum windows versus CIP's shoulder-apex measurement, then demonstrate that gauges exist purely to pass or fail a chamber, not to give you an exact number.

Key points

• Headspace defined: Ray Gross explains it as the gap between the breech face and the shoulder datum on a bottleneck cartridge, built in on purpose so ammunition reliably functions across different rifles.
• SAAMI vs. CIP: Cam shows how SAAMI publishes a min/max range off a shoulder diameter, while CIP measures to a theoretical apex point labeled "S" on its diagrams.
• Gauges are pass/fail: Gross stresses that go and no-go gauges only confirm a chamber is shorter than max and longer than min; they're deliberately undersized elsewhere so they don't interfere with that one check.
• Belted magnums and rimmed rounds: the pair cover how belted magnums headspace off the belt rather than the shoulder, which Gross notes causes brass stretch, and why companies like Peterson built "Long" variants to tighten that clearance.
• Rimmed cartridges: gauges for rounds like .357 Magnum or .30-30 simply check rim thickness, since the rim itself locates the case in the chamber.

Quick take

This is a straightforward, technical sit-down rather than a flashy demo reel, and that's the appeal. Gross's background building reamers gives the explanations real weight, and Cam keeps the conversation grounded for reloaders and gunsmiths who've been confused by gauge terminology for years.

Watch the full video: Ultimate Reloader