Depends, in part, on the age and era of mfg. of your 20 bore. About 1930-ish, 20 bores were chambered for the then std. 2&3/4" paper shells of that era. Also, bear in mind that all 20 bore Smiths "from the git-go" through the end in the 1950's-- were built on the FW frame-- so any express loads would be a possible problem, especially if your Smith has a straight hand style buttstock.
I've been collecting and shooting Smiths for over 30 years, I'll consider a graded Smith 12 bore R frame with a straight hand stock (and 2 triggers) but will pass up a similarly equipped Smith in 20 bore-- not enough timber in the stock head to suit me. RWTF
