Complex sentence: It was in this time frame that the "modern" hammerless designs became common, like the Winchester Model 1912 and the Remington 870 and the Model 1897 was superseded by the Winchester Model 1912.
Split into simpler sentences: It was in this time frame that the "modern" hammerless designs became common, like the Winchester Model 1912 and the Remington 870. The Model 1897 was superseded by the Winchester Model 1912.