Oversized chambers

The German FG42 (Paratroop rifle 42) and some issues of the MP44 make use of the same principle as a fluted chamber in that they have chambers that permit escape of gases around the cartridge case. These chambers, however, are not conventionally fluted, but are of larger diameter for approximately the rear half of the chamber. This allows the gases to escape into this area, thus equalizing the pressure and easing extraction.

A list of some of the more current weapons using these chamber markings appears in Table 4.1.

The depth of the impression left of the fired cases varies enormously with longitudinal flutes leaving the most significant markings, and the helical almost none at all other than the slight blackening from the discharge residues.

The variation in depth of marking produced on the cartridge cases can be seen in Figures 4.19-4.23.

Table 4.1 Some of the move recent weapons utilising chamber markings.

Chamber marking

Weapon

Reason for marking

Longitudinal

flutes

H&K P7 9 mm PB

Ease extraction

Longitudinal

flutes

H&K MP5 9 mm PB

Ease extraction

Longitudinal

flutes

H&K21 m/g 223 Remington/ 5.56 mm NATO or 7.62 x 39 mm

Ease extraction

Longitudinal

flutes

H&K33 m/g 223 Remington/ 5.56 mm NATO

Ease extraction

Longitudinal

flutes

H&K 91 7.62 x 51 NATO

Ease extraction

Longitudinal

flutes

H&K 300 0.22 WMR

Ease extraction

Longitudinal

flutes

12 B Bernadelli shotgun, the Automatico V.B.

Ease extraction

Longitudinal

flutes

Russian Tokarev M1940 7.62

Ease extraction

Scoop flute

H&K4 0.380 acp

Retard extraction

Scoop flute

Seecamp 0.32 acp

Retard extraction

Helical flute

PRC Type 64, 7.62 x 17 mm slp

Ease extraction

Single annular groove

PRC Type 77, 7.62 x 17 slp

Retard extraction

Multiple annular grooves

Kimball 0.30 M1 Carbine

Retard extraction

Multiple annular grooves

Colt National Match Mk III

Retard extraction

0.38 Spl

Perforations

AMT Automag II

Retard extraction

Increased chamber size

German FG42 and some

Ease extraction

issues of the MP44

H&K, Heckler & Koch; PRC, Peoples Republic of Clina; AMT, Arcadia Machine and Tool.

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