This model was also known as the “Famous 12”. It was first available circa 1911 and was manufactured until just after WW2.
The Model 12 was the first of the BSA Small Frame target rifles with a wide target fore-end. The 12 was built on a slightly heavier action than the previous models, the total width of No12 was 1 ¼", as opposed to 1" on earlier models. This wider action was carried forward to the Model no's 13, 15, and 12/15.
The No12 had slight variations over it life time with different rear sights, types of fore-end checkering & different foresights. From around 1930 the cocking indicator was dispensed with.
This example still has the cocking indicator so predates