Bren maagazine, alternative construction

I have a Bren magazine that has the joins between each side of the casing overlapping each other and then spot welded along this overlap in order to join the 2 parts of the casing together. I don't believe that I have seen this method of construction before; is it unusual? All the other Bren magazines which I have seen have the joins butted together with no overlap and then seem welded. There are no Mk designations on it but it does have an auxiliary spring. Thanks for any info.

No just another method of production. Relaxation allowed '......in order to make best practical and economic use of the manufacturers existing facilities' This was the one of the usual reasons given for a relaxation in standards.