Is “Dural” an aluminum alloy?
The short answer: yes.
The somewhat longer answer: Dural is also known as "Duralumin". It is an age-hardening aluminium alloy, whose main alloying element is copper. It was developed in Germany shortly before WWI and has a long history of use in applications including aircraft and racing bicycles, as well as in certain firearms. In drillings it is used for parts like the receiver body, typically with steel inserts for the high stress/high wear areas, and it enables a significant weight saving compared to an all-steel receiver.
There are more modern aluminium alloys of course, and some of these may in fact be used in more modern drillings, but "Dural" has a pretty long history.
