The only MAT anything I could find was the MAT 1949, which was a French subgun in 9mm. If the MAT is all in capital letters that is probably a French designation. The first two letters are Manufacture d'Armes and the last is the name where it was built (MAB - Manufacture d.Armes de Bayonne). The T in MAT stood for Tulle. Of course there are exceptions to this, like all rules.
Germany did produce a series of inexpensive revolvers from the Rohm company and there was an RG-11 listed. This is a 22lr revolver. There is also listed a Reck SM-11. This appears to be a baby Browning look-a-like (sort of). It's a .25 cal auto holding 5 rounds. Seems to also be an inexpensive handgun as only the barrel, striker, spring and pins are steel, the rest is built of sintered metal.
Though this is all conjecture as to whether it helps or not.
If more information is available perhaps we can help out better.