The vast majority of “dual codes” Mauser-Berlin assembled were based upon Astrawerke made receivers coded “bcd”, which represents Gustloff-Werke’s operation at Weimar. They range in dates from 1941 through 1943, though all seem to have been made in 1942 and 1943. These receivers are far more complicated to date than the ERMA “dual codes”, which all fall in a narrow window of production. Apparently Mauser-Berlin took delivery of the first receivers very early in 1942, you see them showing up in the middle of the first block of 1942 production and increase in number through the early blocks of Mauser-Berlin production. Actually, this type of receiver represents the majority of rifles assembled in some blocks. It is far easier to find a bcd/ar 42 in the “b” through “g” blocks than a straight up ar/42 in those blocks. These seem to end in the 1942 g-block, at least for a time, only to show up again in smaller numbers in 1943. During 1943 the bcd/ar 43 dual codes are much rarer, but show up in almost every block between the a-block and j-block (they show up in the b-block through g-block, at least one is known in each block, plus one i-block is also known). Most interesting are the receivers that are not actually “dual” coded, there are several Mauser-Berlin assembled bcd/43 without the added “ar” in the last blocks, the g-block and i-block, which shows that they dispensed with this added feature near the end. The bcd/ar 42’s and bcd/ar 43’s are trickier to date, obviously, the 1943 dated were assembled in 1943, the barrel codes on enough of them prove this, but as the acceptance and serial patterns are nearly identical between 1942 and 1943 production, you really need to see the barrel code to know when a rifle was probably made.
Recently, a question was raised about Mauser-Berlin’s production of the so called “dual coded” rifles, that began in late 1941 and ended in 1943, – the same year Mauser-Berlin dropped carbine (Kar.98k) production to focus on MG42 production.
I thought this would be a good subject for discussion, so examination of known examples follow. It seems that Mauser-Berlin took delivery of leftover ERMA (ax code) receivers late in 1941, when they dropped rifle assembly to focus on MP40 production (They would continue making 98k receivers, though primarily as a sub-contractor for JP Sauer). The first rifles show up in the “L” block of 1941; however it is the “M” block when most show up, mostly late in the block and very near the end of 1941 production. They linger into the first block of 1942 production (no suffix).
Most ax-ar coded rifles were probably made at the very end of Mauser-Berlin’s 1941 production run; though it is likely many were not finished until early 1942. This is because of the characteristics found on the known rifles. First, Mauser-Berlin production serialed both the receiver and the barrel until very late in 1941, typically this changed in the last block of Mauser-Berlin production, the m-block. In that block you will start to see the rationalization changes, ordered by Hitler and imposed upon the German military, to simplify production. This process is best shown in rifle production with a reduction of markings and finish standards that you will see on late 1941 and throughout 1942 production, – it also accounts for the reason ERMA, and later Mauser-Berlin, would be redirected to other projects, and away from rifle production.