Royal Australian Navy: 1911-1927
Victorian Cavalry Regiment 1885-1892
The ball type button for both the Victorian Horse Artillery (Cossum p.15) and the Victorian Cavalry Regiment (Cossum p.16) are very similar. In Cossum’s book the first was made by Firmin of London and seems to have a Queen Victoria type crown, and the second made for Bowley & Co, Melbourne, with what looks like a Tudor (a.k.a. King’s Crown), even though it dates from Queen Victoria’s reign*. Apart from that, the design is the same so I have some hesitancy in firmly identifying the button in case both troops were supplied with the same/similar buttons.
*Victoria had a small diamond crown of a similar shape to the Tudor Crown made in 1870. It was her preferred heraldic crown, but this was not insisted upon.
In Cossum’s book, the button most like this one is the General Service Button of the NSW Volunteers on page 8. Similar, but less so, is the Queensland Volunteers on page 23. I can’t imagine Sol Davies (1881- ) manufacturing uniforms for other colonies as he was not a large concern. He claimed to have a government contract to manufacture clothing around 1930, but the button above has a Queen Victoria crown, not a King’s Crown. Perhaps he supplied some uniforms for ‘Victorian Permanent Staff’ (Cossum page 17) when he was a young tailor before he was married and moved to Sydney in around 1902-1903.
He had a checkered history. See http://www.austbuttonhistory.com/branded-buttons/branded-buttons-tailors-buttons-s-z/