What German intermediate cartridge rifle/carbine is known under the designations MP 43 and MP 44?
Intermediate cartridge:  The first intermediate cartridge to see widespread service was the German 7.92×33mm Kurz used in the StG 44. StG 44:  It is also known under the designations MP 43 and MP 44 ("Maschinenpistole 43", "Maschinenpistole 44" respectively).
StG 44