Welcome to the forum, sir. The DWM means "Deutsche Waffen und Munititions", this is the maker. Th "m" below the serial # is the block series. They were made in blocks using the sns up to a designated number under "a" block, then again the same numbers using "b" block, ect. It kept the serial numbers manageable and possibly estreamlined the production process by using the repeat numbers on the small parts. Mauser used the code "byf". The collector folks here can provide much more detailed info, they really know their Lugers. I just like to shoot them.
rk
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