Suffice it to say, many, many deer are poached every year by guys with .22 rifles, as in .22LR. Not that I feel that it is an adequate round for deer under ANY circumstances (short of SHTF survival), but true nonetheless. The .223 with 69 grain bullets comes up with just short of 1400 ft-lb energy, the 6mm Rem is in at 2100 with a 95 grain bullet, so about 2/3 the energy. No reason the .223 would not be effective for deer with proper shot placement.