These 'bolt, locking' appear in the SAI's, (the Small Arms Instructions) of 1943 somewhere but I'll have to look, to the effect that in order to overcome shortages and bottlenecks leading to stoppages, '........these dimensionally different' locking bolts will be fitted to rifles at the Ordnance factories periodically. So far as I am aware, they were never issued as spare parts through the Armourers system, only at the factories as that simplified locking bolt doesn't feature in the earliest known No4 Ordnance/REME parts list. The post war EMER's did mention it somewhere but can't be bothered to look through now. But suffice it to say, when spare parts were plentiful, it would have been changed as an 'A' class modification or miscellaneous instruction.

As Wheaty says, that locking bolt without the catch just prevents the rifle from being fired which is really as safe as it gets! Although you can still load of course...............

I'm a bit puzzled about its use on the big old tank smoke launcher Wheaty.................. They were only made/based on worn out SMLE actions. Will the No4 bolt locking fit onto a SMLE?