Assuming this is a double triggered Smith, and of course, a Featherweight series (FW or FWE)- here's what I would do- get a set of 20 gauge snap caps, put a 1 ounce load in the right barrel and a snap cap with a peice of masking tape over the primer in the left barrel, and test fire it- then do the reverse, firing only the left barrel with the one ouncer and the "dummy" taped snap cap in the right barrel- to check against possible doubling from the extra recoil "jar" of the King Konger loads in a light 20--

"The field is the touchstone of the man"..