Headspace and Walther KK300

[tim s]

Simon,

Headspace in a .22lr is the gap between the bolt face and barrel for the case rim. Target rifles have the headspace set at, or near, the permitted minimum (0.043in under CIP and SAAMI spec). This ensures the bolt pushes the rim flush against the barrel face, so when the case is struck by the firing pin the primer is detonated instantly. When there is excess headspace the case isn't chambered fully until hit by the pin, which saps energy, and can cause inconsistent ignition.

Cases that stick are more likely to be caused by a tight match chamber, especially if the barel and bolt aren't regularly cleaned, than by headspace. Remember the bullet actually engages with the rifling, and is finally jammed in as the bolt locks. Unloading an unfired cartridge can be tricky if the chamber is very tight. A bolt that's set for minimum headspace will feel a little harder to close, because it meets the case a few thousands of an inch sooner tHan an okd and worn bolt with a little excess . However if headspace is set very tight to suit Eley, then the bolt may only just close on Lapua and RWS, as the rims are thicker. I would not expect a Walther ( or Anschutz, or FWB) to be this tight from the factory, as they seem to headspace to 0.043-44in. But it's not unknown when a gunsmith has replaced the barrel, as headspace is often set tight, at 0.041-42in.

Headspace can be tightened with shims on some rifles. These slip over the bolt body, under the handle. Barry Nesom sells shims for 50p. When a rifle has excess headspace through wear, rather than when the owner wants it super-tight, a new bolt handle is a better long term solution. Opening headspace can be done with a chambering reamer, which relieves the barrel face, or by fettling the bolt handle. Both are jobs for a professional gunsmith, one who is experienced with smallbores. The KK300 has the barrel secured with epoxy, so it can't be moved unlike early KK200s and Anschutz 2013s where the barrel is clamped into a split receiver.