FAL and L1A1 threads: a wild ride?

[Bruce_in_Oz]

There seem to be many interesting thougts on the type of screw threads used on these.

Some claim that the L1A1 breech thread is Whutworth form and so on.

My thoughts:

The L1A1, (Brit and Oz) and the production C1, Breech thread is, and i quote from an actual barrel drawing:

1" - 16UNS-2a

One Inch, sixteen threads per inch, Unified National (S) Special
Major Diameter: 0.9985 -0.0094"
Pitch Diameter: 0.9579 -0.0050
Minor Diameter: 0.9218 MAX

Muzzle thread:

9 / 16 x x24 NEF (National Extra Fine).RIGHT HAND thread.


Other things

The rear-sight adjusting screws are BA. FAL rear-sight adjusting (zeroing) screws are Metric.

L1A1: 3BA
FAL: M4

Because BA threads were derived from a metric thread, (Swiss Thury clock-makers "specials"), there is SOME commonality, "Zero" BA is basically M6 complete with one MILLIMETRE pitch, but with a 47.5 degree thread form. You can often run one into the other, but it will eventually get "untidy".

Why are the L1A1 lateral adjustment screws BA? Because it was a STANDARD thread across the Commonwealth and its pitch was "close-enough" Why not keep the metric thread? Not done, old chao. The VERY British (and Commonwealth) BA would provide "close-enough" lateral-deflection, per turn increment

Bear in mind there there are also US-type threads in the L1A1. The 1950s were "interesting" years.

When the Rifle Steering Committee got to work on the L1A1, they made as few changes to component dimensions and tolerances as possible. You can plug an entire L1A1 receiver group onto a FAL trigger-mech housing and it will lock-up correctly and actually function Some smaller parts are "different" (gas system variations are a bit of a challenge), but there is an unsurprising amount of compatibility.

The same sort of "creativity" went on the the development of the L7 GPMG from the MAG 58

At one stage, Oz had both types in service, but, quite some tome ago, went fully metric and it is possible to find some very interesting component and marking combinations on these venerable old guns.

ALL of this happened under a "closed shop" operational and maintenance regime.

If the gun-plumber needs to replace components, a parts request goes in and eventually, the correct bits would land on the workbench; no popping down to the local hardware store for a few bags of screws and such.

Information

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[bigduke6]

The oldest L7 I've worked on was from 1964 or 65, definitely pre 66......although a bit like Triggers broom it was still a serviceable weapon. When I was in BATUS the main stay of L7 variations were H&K Made, did a lot of barrel fitting and serial number stamping then...... Think out out of all the ones that come through the Armourers shop at that time, only Two required some work on the rivets.

If anyone is lucky enough to have a L7 and a MG 42 on the work bench at the same time, have a good look at the bipod and the trigger mech........