This must be done before reassembly. By the term " head space " is meant the distance between the face of the bolt and the base of the barrel. When correctly adjusted the face of the bolt should firmly support the base of the cartridge in position in the chamber when the gun is fired.
too much head space (i.e., adjustment is too loose)
The base of the cartridge will not be firmly supported by the bolt face and when cartridge is discharged a separated case or a bulged case may result, causing difficult extraction.
too little head space (i.e., adjustment is loo light)
(This can sometimes be detected by ear when the gun is being fired, as the bolt on its return to its forward position will give a dead sound effect.)
Binding of certain moving parts and slow rate of fire may result. It may not be possible for the mechanism to go fully home to the firing position, when the gun cannot be fired. Breakage of the barrel extension can result from firing the gun with head space too tight.
the correct head space adjustment
(a) Partly screw barrel into barrel extension.
(b) Remove extractor from bolt. With barrel and barrel extension in a horizontal position, place the bolt in its full forward home position in the barrel extension.
(c) Lock bolt to barrel extension by lifting breech lock up into its seat; hold it firmly in this position.
(d) Continue screwing barrel into barrel extension untiJ resistance is felt (other than that of the barrel lock spring).
(e) Release breech lock which should now fall of its own weight, if the head space adjustment is correct.
(f) Remove the bolt.
(g) Note position of barrel lock spring ; if this is in between two barrel notches, screw barrel up to sccond notch. If barrel lock spring is seated in a barrel notch, screw barrel up to next notch.
It is advisable to mark barrel with this correct head space adjustment so that quick head space adjustment can always be made on subsequent stripping and reassembling.
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