Found it!

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I had given up looking for the biggest gun on a tank, or sorts.  But was still looking through videos regarding tanks.  I'm not sure I would have wanted to be a tank man.  To me, that would be claustrophobia inducing.  If that got hit, there would be no place to go.  And, inside, I would guess there would be little room, less so for taller guys.

Yep, a 183 mm gun, or 7.205 inches.  I guess I thought it would be bigger.  Then again, 16 inch guns are battleship sized, so not sure what I was really hoping for?  Just, a curiosity that got me to looking.  But, yes, tanks are fascinating, and terrifying, for and against.  Now, though, I know just how big the biggest of guns were.  They say that they are just hitting 140 mm guns now.  Between advancements in projectile tech, and else, they are able to get more, from less.

Back to... something else... or... nothing.  Later.