many people shoot much lighter projectiles with great results on deer size game. I think you need to get some other projectiles and try them out in your rifle, and find one your gun likes and you are comfortable with, shooting at deer.

Personally, 80% of the time I shoot s 230 grain roundball out of a .54 caliber sidelock for deer. The other 20% I shoot a 300 grain conical which I make from a mold. Both projectiles will take deer down where they stand. Shot placement is the key thing as I am sure you are well aware. Good luck hunting, and have fun shooting the rifle.