My never-ending quest for odd British WWII equipment information has led me to consider small arms ammunition. British and Commonwealth factories produced mountains of ammo in the standard calibers, those being .303, 7.92mm, .380 revolver, 9mm. I imagine some 15mm Besa, .5 Vickers, .455 Webley auto, .22 Long Rifle, and .455 revolver was loaded too, and possibly .50 Browning as .50 Browning guns were used on some British-made aircraft late in the war.
So far, so clear. But my poking so far has shown that the British and CW forces used a wide range of non-standard small arms during the war, many of them in odd calibers such as .32 ACP (Colt pocket automatic, Webley autos used by police, Llama autos used by SOE), .380 ACP (Colt pocket auto again), 7.63mm Mauser (handful of Mauser and Astra autos acquired in Belgium and Shanghai), 9mm Browning Long (Webley auto used by South African and other imperial police forces). Some .32 caliber revolvers were acquired in the US (Colt, Harrington & Richardson, and Iver Johnson). I imagine these were probably in the common .32 S&W Long or Colt New Police, but I am not certain. There were some .38 Special Colt and S&W revolvers, too, and a small number of Colt Super automatics in the .38 Colt Super ACP (not the older less and less powerful .38 ACP). I even have references for stray pistols in .38 Colt Long (old Colt Army Specials) and .32-20 Winchester (Spanish G.A.C.), and .25 ACP automatics were used by SOE and aircrew.
Enormous quantities of ammunition for the US guns were imported during the war, but I wonder if any of these odd rounds were loaded in the UK and Commonwealth. Some of these calibers (.25, .32, and .380 ACP, 7.63mm Mauser) were common commercial rounds as well, so British and CW production of them on some scale before and during the war would not be surprising. (I am pretty ignorant about the UK and CW ammunition industry in this era.)
During the course of the war Britain also found itself supplying the forces of a number of Allied exile governments. Of these, the French, Belgians, and Dutch had large colonial empires with local forces still carrying native-pattern weapons. Some re-equipment with British and American arms was eventually done, but I know that the French at least always retained some of their older weapons and so did the KNIL in Indonesia. So, was any ammunition for these old foreign guns loaded in UK and CW factories? Local stocks must certainly have gotten depleted as the war went on. The rounds were:
Belgian: 7.65mm Mauser
Dutch: 6.5mm Dutch Mannlicher, 9mm Browning Long
French: 8mm Lebel, 7.5mm MAS, 7.65mm Long, 8mm Lebel revolver
And then there’s the .320 Revolver cartridge. I don’t know if any of the Webley revolvers chambered for it were used as service weapons, but with SOE and the Home Guard you never can tell…