After a number of issues had been discovered, including a serious problem with rusting gas tubes, the existing stocks of the rifle were modified between 1953 and 1956, and the reworked rifles were designated Ag m/42B.
其後，這些步槍被發現出現了一些問題，包括於當中嚴重的問題是生銹的導氣管；1953年至1956年之間，將現有的步槍庫存都進行了修改，並將重新設計的步槍稱為Ag m/42B。