I think I have found the minimum bullet weight in the 223 Handi, SS, normal barrel that I own.  I have tried the 223, 40 gr JHP and find it is NOWHERE near as accurate as the Winny White Bx 45 gr, JHP round.  
I shot 40 rounds of Federal 40 gr, JHP, 5 at a time, with a 100 yard stroll and back between each group and back.  They are/were all over.  I swear I think I saw the beginnings of 'Key Holing' on some targets.  Went back to the 45 grain and viola! all is forgiven, come home.  Anyone else have/know of this weight being unstable in a 1 in 12 or is it just me?