MG42   bolt  catches

 

  

 

 

The reason for the implementation of the bolt catch is safety. It helps prevent the gun from prematurely unlocking due to harmonics in the roller/wedge system. The early type catch was introduced in about 1943-44 after extensive high speed camera work and other tests detected the harmonic problem that was inherent in the locking system.

If you have a MG42 with the early bolt group that has no catch, it's highly recommended to get a bolt group with the catch, as an "out of battery" firing can cause severe injury to both persons and/or property.

  

 

 

The above and below picture shows the three different types of bolt catch that can be found in a MG 42 style machinegun.

1.    Early type-WWII bolt catch with wartime ejector bar.

2.    The center bolt catch is the early postwar type found on both the 8mm and the .308 guns.

3.    The catch on the right is the current production MG3 type along with a current production ejector bar.

 

  

 

   It may be noted that the wartime catch is longer than either of the others and when installed (in either direction) it loads the locking wedge. Normal installation is with the small diameter end to the rear of the bolt. The second type can be used with early type ejector bars if it is placed with the small diameter end to the rear. It does not load the locking wedge at rest in this position. If used with a new type ejector bar it can be placed with the small end forward and the locking wedge is loaded at rest. The manuals I have seen state that the catch can be used in either direction. The late type catch is used only with the late type ejector bar and according to the manuals it loads the locking wedge by inertia as does the second model when placed small end back. Apparently this is sufficient to prevent the dreaded " out of battery firing". The bolt catch has been mistakenly dubbed a rate reducer, as this is a side effect of it's installation.

Thanks to Frank Hatten who provided this info and pictures.