If you are going to try to get 2,600 fps out of such a short barrel, instead of your original idea of a slow bullet, you are back to just shooting normal .308 Win 150-gr loads, of 2,800 fps from a 24-inch barrel.
As to richochet, at close range, the bullet will striking hard ( like a normal load at 100 yards or less), so it is going to upset and mushroom, and that is what is going to exit the animal and strike the ground, so little chance of much richochet there.
.223 FMJ bullets will ricochet off a windshield of a car, head on. So will FMG 9mm pistol bullets. Police bullets designed to not richochet off glass and hard floors, like the Hirtenberger 9mm, flatten out at whatever angle they hit, and go through glass, but just sort of slide along a tile floor.
That's why I would go with something like a 150-gr FN .30-30 bullet at 2,400 fps or even less. In a .30-30 lever action up close, it has killed large bear, moose, elk, and angry cornered boar too numerous to count.
I have killed wounded deer, up and on the move, with 9mm and .38 and .357, all one shot to the chest, so the above .308 load is way enough. Go borrow a .30-30 and shoot in the dirt with rocks around; that's a cheap way to find out if it will work for you. Talk to the .30-30 hunters here at SD.