One of the problems with running Belgium and the Netherlands in Wesworld is the lack of OTL parity. Both nations were strongly effected by the Great Depression, the Belgians sank their $ into forts, while the Dutch relied on neutrality and starved their military. Then their military history ceases in early 1940. Here the Dutch are far richer and quite militaristic, and the neither Kingdom is in a depression (Belgium had one 1933-35 or so).
So, the Belgian Self Loading Rifle came to the Cusp of entering service..and didn't. It then became the SLEM-1, then the SAFN-49, then the FN FAL. Due to the war interruption, the wesworld introduction of these rifles will be faster than historic.
OTL History of the Belgian Self Loading Rifle
Developement started in 1936 by Dieudonne J. Saive of Fabrique Nationale
Prototyped in 1937.
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Ready for production Late 1938-Early 1939 with a 5 round clip. *
Production Deferred 1939.
Belgium invaded 1940.
So part of 1939, 1940,1941,1942, part 1943- no further development
Research continued 1943 at Enfield
Late 1943 adoption of 7.92x57 leads to :
1944 prototype of SLEM-1, a 10 round bullpup design note <1 year after research restarted
7.92x33 Kurz round leads to further work.
Late 1944, Return to Liege, where Germans had stripped FN of machinery.
It seems reasonable to presume that little work occurred until the end of the war, in mid 1945
So presume Late 1944-Late 1945 no work
1947 FN 49 prototyped , FN FAL prototyped
1948 contracts given for FN49, FN FAL demonstrated, redesigned for Bullpup in 0.280.
1949, May 31, first FN 49 delivered. Conventional pre-war, high quality, high cost build.
1950 FN FAL in competition, redesigned for 0.30 'Light Rifle'.
1951 FN FAL formally introduced in 7.62 x 51
So... Since the war "cost" at least 5 years of development time, plus 1-2 for changing cartridges I propose the following schedule.
1938-39 - Belgian Self Loading Rifle ready for production.
1940 - SLEM-1 Available
1942 FN- 49 available
1944 FN FAL available.
*Long ago when I was setting up Belgium, I found a reference to the rifle being adopted for service, but not produced. Wiki cites the Sept.39 outbreak of war as behind a decision to continue producing standard rifles and MGs, rather than starting the SLR40. See SAFN-49 article.