Note the gun is "Not" Out of Proof with thin barrels "IF" it was proofed with those thin barrels.
It "IS" out of proof "IF" the bores have been enlarged beyond the legal limit without it being re-proofed, thus producing the thin barrels After Proof.
Very often this is the case on guns having very thin barrels.
Such guns are not illegal to sell here in the US, Caveat Emptor.
They are illegal to sell "OR" Export in countries with proof laws.

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