Up in the sticky's at the top of the forum is a sticky called
Safe loads and cannon plans. Look there and you will find a chart from Matt Switliks book "The More Complete Cannoneer" for cannons under 2 inch bore. Look you bore size up there.
The load from that chart is the maximum recemmend load and you should reduce the load substantially to start especially if using lead balls.
Your ball is a bit tight for the bore, another reason for a substantial reduction in starting loads. Make sure you have a bore gauge and you check every ball with the gauge before using it your cannon.
The rule of thumb ball diameter for your bore is 1.212. The rule of thumb for windage-the difference between bore diameter and ball diameter is 1/40th. Divide bore by 40 and multiply by 39. In your case 1.243/40 = 0.031075 x 39 =1.211925
