Very Confusing GP-11 and Go Gauge and Case Headspace Differences 3 Rifles (phew)

[Bruce_in_Oz]

Swiss chambers are interesting.

The chamber on a G or K-11 has a LONG throat. This is primarily so that remaining supplies of the old "torpedo" GP-95 could be safely chambered and fired. There was also the equal "bonus; the generous freebore kept peak pressure down with the somewhat more lively GP-11.

By the time they got to producing the K-31, the old ammo was merely a curiosity, thus these rifles have a short throat.

As anyone who has tried to brew handloads for the K-31, using Sierra Matchkings will have discovered, the throat IS very short. SMKs have TANGENT ogives.

The GP-11, having a SECANT ogive and a VERY short "parallel" bearing surface works perfectly with this short throat; i.e., the cunning Swiss chaps designed their new rifle AROUND the exquisite GP-11 cartridge.

There is usually VERY little "variation" in the headspace of correctly maintained K-11s or K-31s.

If you think you've seen some odd chambers, take a close look at the StG-57 / PE-57. Unsurprisingly, in the 1950's, the Swiss came up with an idea that has recently resurfaced in the odd little FN 5.7 x 28; "creative case bulging", to reduce back-thrust on the bolt and retard extraction a few microseconds until peak pressure has dropped.

In pretty much all military systems, the fired brass cases are NOT reloaded, but recovered for their scrap value. This neatly avoids the potential hazards of cases "failing" on a two-way range, at extremely inconvenient moments. Steel cases, which must NEVER be used in a Sig PE57 or SiG AMT, are generally regarded as "biodegradable".