When our North American ammunition companies introduced rifled slugs circa 1938, they came in 12-, 16- & 20-gauges and .410-bore. Remington Arms Co., Inc. introduced their Model 11-48 in 28-gauge and .410-bore in 1953, and by their 1954 ammunition catalogs they had added a 28-gauge rifled slug load.
Remington 28-gauge Slug mouth.jpg
Remington 28-gauge Slug head.jpg
The 28-gauge rifled slug offering was dropped as they phased in their plastic hulls in 1961 and 1962.