Interchangeable parts

With all the 303's made with say the No 1 Mk III and the No.4 types I would like to know app how much can be interchanged between them.
Like the Butts, sears, screws, pins, bands etc as the No.4 was in the pipeline pre WW II and won out over another weapon due to how far along the development of it was.

But it seems funny that the Brits in designing the two types did not get down and utilise 100% of the non important stuff like screws etc.

I mean you cannot fit a Mk III mag unaltered into a No.4 and vice versa I thought expedience was the essence of arms production in a time of conflict.
And to have the No.4 utilise say 80% of the No 1 Mk III like wood (just shape it a bit differently) stock bands, screws, sight blades, trigger guards and so on it may have helped getting the 4 out quicker.

It is only a general question and I am sure the explanation goes far deeper that my rudimentary question.
I was told the Japanese 7.7 round could not be fired in a 303 but the opposite was true of the 303 round in a Japanese rifle even though the 303 was a much shorter round.
I mean in the jungles of PNG where the ranges were down to mere feet who really cares about accuracy and using the enemies rounds if they worked in your weapon :confused:

One area where a 'saving' was made was in the change of threads on nuts and bolts

The old No1 Mk3 used a unique "Enfield Inch" thread - to save time and cost the No4 used standard, commercially available, BA threads with a couple of BSF and BSW hreads.

Just one example of the change is with the front trigger guard screw :

No1 Mk3 = 0.25" x 30tpi
No4 Mk1 = 1/4" BSF ( 26tpi)

The Enfield design is largely due to accidents of history, as with many things.

Britain had very small standing armies up until the time of the Boer War, and its firearms had been an evolution from the days of (literally) hand made muskets. The gunmaking industry had developed its own specialist components (eg fine-thread screws) in advance of- and separately to- the process' of industrial standardisation started by the likes of Whitworth (ironically, of course, a famous firearms inventor as well as industrialist!). The main British arms design authority - Enfield - was of course itself a traditional gunmaking entity, and it had usually been able to meet the rifle production quantities needed by the small armed forces.

The Long Lee was supposed to be the last of the "bench made" rifles from the traditional side of gunmaking. Britain was caught out by the large troop mobilisations needed for the Boer War, and bottlenecks in mass rifle production became obvious. Although the No1 rifle was developed and issued, it and the P13/14 were really little more than short-life large scale trials rifles. Had WW1 not occurred, probably a more modern weapon would have been selected, designed and production-engineered to use standard industrial methods and components (eg BA thread screws). The rest, as they say, is history: no-one ever expected to have to make 4 million No1s with archaic design features!

The No1 MkVI and No4 were themselves little more than a make-work design study for Enfield - test beds for production engineering. As with the No1, there was no expectation that the No4 would ever be issued, but that a modern semi-auto would come along when designs matured and politicians freed up some cash.

Incidentally, the receiver and bolt geometry of the No1 and No4 are identical. Components that can be switched are: cocking piece, firing pin, sear, sear spring, magazine release catch, trigger, magazines (sort of...).

T/Box - I think that the striker is only interchangable if you also change the cocking piece (ie cannot be 'switched' as individual components)

The striker threads (as it happens) are the same as the Front Trigger Guard Screw ie :

No1 MkIII striker is 0.25" x 30 tpi
No4 Striker is 1/4" BSF (26 tpi)

I meant that they were dimensionally identical, rather than absolutely identical.

I wasn't going to spread horror stories about trying to match up strikers and cocking pieces..... but..... I'm sure that i'm not the only one who thinks that there are more than just two different threads involved. After hours of attempting to match up strikers and cocking pieces, I seem to have about four unique combinations that will not interchange with any of the other three!