You should have 1700 depending on barrel length.
You can go up to about 95 gr with that weight
of slug/ball. Could you mike a new unfired case
just above the rim, and measure a fired one.
We use that as idicator of how high you can go.

Some more slug and sabot ideas folks are doing.

First is a long pointed slug with locked on base,
It goes to target with base,can work smoothbore.

Second is picture of Hexolit sabot base slug
with petals expanded, sure would make bad wound.

Third shows a variety of Gualandi slugs you can
get for reloading, and we're finding that these
locked base slugs, Brenekke/USS style slugs, are
giving good accuracy in smooth barrels which can
save when doing heavy barrels.Weights shown in
grams, get our weights in grains multiply by 15.4..Ed