It would be helpful to post what kind of bow you are shooting with and at what speed the arrow is traveling if you know it.

I will assume that the arrow is about 29 inches long with 4" vanes. That arrow will weigh about 525 grains. I would guess (assuming a newer bow) that your speed would be about 230 fps or so.

That set up has plenty of energy to pass through an elk at 40 yards never mind a whitetail deer. A big heavy arrow like yours is hard to stop and the stinger on the end only aids penetration.

If you are accurate at 40 yards and you know the distance to the deer then I wouldn't hesitate to shoot a deer at 40 yards with your set up.

You will start out with about 62 foot pounds of KE at the bow and at 40 yards you will still have about 55 foot pounds of KE.

I am certainly not advocating you do this but that arrow will still have sufficient energy (about 50 ft lbs) at 100 yards to pass through a deer.