Headspacing a .22 LR for Lapua, SK, Eley & RWS

In a rimfire, the rim is the headspace surface. Get the crush on that rim consistent across your ammo lot and groups tighten; leave it sloppy and you chase fliers you'll wrongly blame on the wind.

What headspace is in a rimfire

In a rimmed cartridge like the .22 LR, headspace is the distance from the bolt face to the rear face of the barrel — the surface the cartridge rim bottoms against. Less the rim's thickness, that gap is what the firing pin has to cross before it crushes the rim against the chamber edge and lights the priming compound. The rim is the headspace surface, which is why rim-thickness consistency and headspace are two halves of the same problem.

Match ammo isn't identical

Lapua, SK (its Nammo sister), Eley, and RWS all hold tight rim-thickness tolerances by industry standards — but each maker, and each lot within a maker, sits in a slightly different band. That is why you re-measure when you switch lots and never mix brands mid-tune.

The sweet spot is consistency, not minimum

Optimal headspace is the dimension that delivers consistent rim crush across the whole rim-thickness population of your chosen lot: small enough that the firing pin's crush is repeatable, with enough clearance that the bolt still closes on the thickest rims in the box. Chasing zero clearance is a mistake.

Measuring what you have

Three approaches: go/no-go gauges, step gauges, and sorted ammo used as a reference stack. Whatever you use, don't trust one reading — take three, rotate the gauge, and average.

Adjusting with shims

Two levers: move the barrel or shim the bolt. On the CZ 457 — one of the most popular rifles on the line — a V-block clamp holds the barrel at variable insertion depth, which is the primary headspace adjustment; and its bolt is famously shim-friendly, so you can add a shim behind the bolt face to reduce headspace by the shim stack. The Bergara B-14R follows the same idea with a Rem 700-pattern bolt and removable head. Bolt shimming is often the more repeatable route: no disturbing the barrel-action interface, no barrel removal, no gunsmith.

Cautions & pitfalls

Don't shim past available firing-pin protrusion, watch for rim deformation, and re-verify primary extraction after any change. The usual mistakes: ignoring rim sorting, mixing brands without re-measuring, over-torquing the V-block, chasing zero clearance, and skipping verification after a shim swap. After every headspace change, function-check with sorted ammo, confirm with a gauge, and live-fire test. Questions? Bring the rifle to a match — the community is the point.

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