While a .30-30 will probably work just fine for you, you're going to be limiting your range.The Marlin is a great gun, but I'm not sure you should give up on your '06. If it shot well before, and nothing was done to the gun, it should shoot well again. Have it checked out by a gunsmith or someone who is familiar with the model. Maybe mounts are loose, maybe you need a new scope, or maybe you should try a different load if you can't get your current one to group.