11b box stamped says 43.3 CU. IN

[acelectric103]

Due to splices I need to make, I need a box to be at least 42.5 CU IN and most all of the boxes I see are only 42 cu in.
At home depot the Steel City square 11b's have it stamped saying 43.3 Cu. In., but when I look at the Steel City website and online informational specs they only claim it is 42 cu in. Seems to me if i go by the stamp then I am OK.....any ideas on this discrepancy?

You can try some plaster ring.