Can't comment on the frame size, but I have owned one each Browning Standardweight 16 and two each Sweet 16's. Before I get to them, I'll go to Browning advertising copy, as included in the 1940 Shooter's Bible. That publication separates Standard 16's from Sweet 16's. Refers to the Sweet 16 as being a "special lightweight automatic shotgun", about 6 3/4#. One weight saving measure is a narrower raised rib on both solid and VR guns. Standard 16 listed at 7 1/4#. And from the introduction of the 16 until 1940, chamber length on both types was 2 9/16". Thus, if you want an A-5 16 and don't want to shoot short shells, beware of the early ones.
Now as to weight, on the guns I've owned, taken on the same digital postal scale: Standardweight 16, 28" barrel, solid rib. Weight: 7/12. Sweet 16, 26" barrel, vent rib. Weight: 7/0. Sweet 16, 28" plain barrel. Weight: 6/14.
I cannot comment on frame size, since I never owned a Standard and a Sweet at the same time. But per the above, I can certainly comment on weight. Whatever weight reduction features the Sweet 16 has, I'd say they will result in about half a pound less weight (per the Browning material from the 1940 Shooters Bible), assuming a gun with the same length barrel, same type rib, factory stock. (All of mine had unaltered factory wood.) Note that of the 2 28" inch guns, the plain barrel Sweet has nearly a pound in weight advantage over the Standard. Add in a few ounces for the solid rib on the Standard and you probably have just about that half pound difference in favor of the Sweet.
