40 is legal in Tennessee (home of the hog rifle).
36 is actually legal in TN.
But let us NEVER confuse legality with morality or sportsmanship. They generally start out with some relationship one to the other, but after the law makers get done mucking it up...it's often nonsense. Use your own good judgement.
SO I may have a 40 completed before deer season ends this year and HECK yeah I'll put it on a deer, given the time and place and shot. BUT when i'm hungry (failed to connect last year) for venison and want to be able to reach out a little further, then the 54 is going to be in my hands.
The 40 i'm building is for squi____ (my dog is watching me type, don't need to rile him up) targets and everything else primarily.
If i had to hunt (deer) only with a 40, I'd keep myself in tight cover* and maybe elevated more for the closest shots--just like with archery tackle, where elevation can contribute to a "bottom side" exit wound for tracking if necessary. *I've only taken a handful of game over 90 yards in all my years (with pill pushers), so "limiting" the range really isn't difficult in these SE hardwoods and cedarbushes.
Ultimate range is going to be a function of the shot presented and the load in the pipe and the skill/confidence of the shooter. Skew that to the short side and i have no problems with it.
The only deer i ever lost to a firearm of any flavor was to a 50 at 80 yards standing broad. (he survived many more years, but never presented another shot).