No4 Mk1* Malfunction

First check the bolt holding the spring to the receiver! This thing can play Old Hob if it even slightly loose.

The safety lever (which includes the shaft) is a multi-start thread in the "safety catch", the little comma shaped do hickey down inside the wood that is moved in or out of the bolt raceway to lock or unlock the bolt & pull the striker slightly off the sear face.

There are two "close but no cigar" mis-setiings you can use which will cause all sorts of odd malfunctions.

Quick way to check.

Remove the bolt & magazine.

Look down & forward into the rear of the bolt channel & wiggle the lever ON & OFF.

You should see the "D" shaped shaft rotate from flat face up, flush with the raceway bottom, & the sliding "finger" in the lefty side receiver wall at 9 o'clock retract fully & completely. Or the flat of the "D" protrude into the raceway where it mates with the cuts in the cocking piece to immobilize it. At the same time the "finger at 9 o"clock should protrude fully into the bolt raceway (about 1/8").

If that's not happening remove the safety, by unscrewing the bolt securing the spring & pull outwards. check the edges of the "D" & the "comma-shaped" catch. & the 2 openings in the bottom left side of the cocking piece. If that's all good clean & lube everything. If any edges are chipped or burred replace the part.

Re assemble the safety catch on the safety lever aligned with the correct thread so that fully screwed down onto the shaft till it stops it aligns like this:

 So it was indeed the safety causing this issue, firstly the spring screw was not snug, second, the timing was off by a thread causing the upper and lower lugs to be ever so slightly proud od the bolt channel.

 The lower lug has become slightly chamfered so I should probably replace it. Though it still locks and removes the bolt off the sear, but that`s probably a poor excuse not to.

Thanx Shamu, for pointing in the right direction

Glad to help