Wow that is impressive, and stacking prbs is something to consider.
You better check the laws in your state. It's common that the states stipulate a single projectile in ML or "primitive" season, and some stipulate a single projectile in any season.
Now (iirc) Alabama considers any single shot rifle as "primitive", even breechloaders, which I think is why you're allowed a caliber at .40, when a lot of other states start at .45. Maybe I'm thinking about Mississippi, not sure.
The first part of the equation is accuracy, of the rifle and you. It doesn't matter if the rifle is a .72 Pedersoli Kodiak double-rifle, if the load isn't accurate, or if the target is beyond the range where you can deliver an accurate shot..., the rest of the discussion is moot.
The .40 will do quite well, and one does not need them at handgun range for that to be true. The .40 tends to come out screaming fast, so tends to have a very flat trajectory. A lot of us use them out to 75 yards, and we don't spend all day tracking down the deer. I think, though I've not taken a poll or anything, that most folks with a .40 take the deer at around 50 yards or less, and I think that's true for larger calibers too. NOT because the rifle and the load can't get the job done, but because the shooter's vision and the iron sights make harvesting deer at that range or less much more successful.
I would not rely on "blood trails" as the primary method of finding a deer; perhaps there is a marksmanship problem rather than a problem with the hole being too small. :idunno: IF the brush is very tight that the deer can go a short distance and disappear, I'd submit that to get any shot at all the animal is very close to the hunter, and so you'd be well within the closer ranges that so many folks attribute to the .40, right?
I make the accuracy and blood trail assertion because you can switch to a lead alloy with a patched round ball in the .40 and get a better chance at a pass through shot (on the lungs) at longer range. The velocity would be higher as an alloy .390 ball would be a tad lighter than all lead, AND it won't deform upon impact as would all lead. You can also, as one reply demonstrated, switch to a paper patched conical bullet and in effect mimic at under 100 yards some modern cartridges that are proven, 20th century deer killers. Anecdotally, out of more than a dozen deer that I've harvested, I only had to track two, and they were hit with a .54 and there wasn't a blood trail. The rest fell within sight of the location where they were hit with the ball. Take out the lungs, and they normally don't go very far. :wink:
I've recently dropped my charge in my .40 down from 40 grains to 30 for small game. This allows me to up the load to the Maryland legal limit of 60 grains using a double powder charge using the same measure.
LD