405grs of shot?

[12GA guy]

For the mathematically brilliant, of which I'm not one, what is a equivalent oz fraction to 405grs of shot?

I was opening up a few hand loads to test them for powder weight, shot weight, and to examine the type of wad used etc., from a flat of shells that a fellow gave me prior to moving back east. I wasn't about to shoot them without pulling at least one or two shells from each box to se how his drops went.

Now the powder weight was fairly consistent with 19.4 to 20gr of Red Dot, if you can call that consistent. The lead weighed 405grs to about 417gr. Hard to be perfect with reclaimed shot I know. Pretty hot loads I'd say, but shootable. He loaded for sporting clays and liked velocity.

Ok get out your calculators..what shot weight was he trying to achieve? 15/16oz, 7/8oz..?