Some 40+ yrs ago I bought a field grade 20ga Flues. At the time I knew not of their reputation for cracking frames & it was marked "Smokeless Powder Steel" so for several years it was fed a regular, steady diet of 2½-1 oz loads. gun had 26" bbls marked 2 & 4 with little choke, an obvious cut down, probably from 28". It served me well for those years of use & never cracked. I have often wondered since after finding out about the frame problem, just how much the actual fit of the top bolt on individual guns played in the frame cracking equation. I never checked the fit on that one, perhaps it snugged up nicely & helped support the frame bar.
PS; It weighed an even 6lbs as I recall.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra