The Sweet Sixteen is a specially lightened 16 gauge Auto-5 which debuted as a test-market item in 1936 and went into regular production in 1937. Only about 4 ounces of weight was saved over the standard model, so it was more of a marketing gimmick than anything else. Here are two similar versions. The top one is from 1938 and still has the 2 9/16" chamber. The bottom is from 1948 and is one of the early 2 3/4" guns.