Too many unknown factors to allow a prognosis. Bullet fit? Bullet alloy and hardness? Gas checked?
Have you read one of the iterations of the Lyman cast bullet manual? If not, do so.
All that said, 1600fps is a walk in the park. 4198 may be your friend, maybe not. I would prefer 4227, RL7, 5744, or my all time fave 4759 but that stuff ain't no more. Trail Boss will get you there but pressures spike quickly when you push it past cowboy action type loads. I don't care for it one darn bit and accuracy always sucked compared to other powders. YMMV though.
As a rule of thumb without going through all the rigamarole of chamber casts and bore slugging, size it to .310", lube it well, and pick a powder from the manual that'll give the desired velocity, and see what happens. At that speed it shouldn't lead unless you're doing something particularly offbeat.
Do yourself a favor and get a neck expander die from either Lyman or RCBS that will expand the neck to accept the larger bullet and bell the case mouth slightly to ease insertion of the bullet. Fairly critical, that. Those dies are cheap. Using a standard neck expanding plug just doesn't cut it- something has to give and it won't be the brass. Your carefully crafted relatively soft cast bullet will suffer as will your accuracy.
