If the conical is too loose there is that possibility of it slipping off the charge. I like at least a bore sized projectile conical. In my .504 White I shoot a .5045 conical. They do not slip. A .503 I can shake back off the load. Also when you actually fire the projectile it expands the base of that conical, roundball, what ever and that in turn grips the rifling of the barrel on the patch out of the barrel.

If you ever doubt the integrity of the conical on the load, turn it over and tap the end of the muzzle on a block of wood lightly. See how far the conical moves off the load. Now I do not mean pound that muzzle end on a block of soft wood (a pine 2x4 works great). Simply take into consideration how much jarring a rifle takes as you walk through the woods. Also if you get to a point where you want to stand hunt, take a ramrod and check your projectile to make sure it is still seated. I do this all the time with sabots, conicals, and roundball.