I would keep the range in the 100 yard area. Certainly not more than 125 yards. The 7.62x39 may kill at longer distances, but it would be a chancy thing on deer sized critters and you would have to be real sure of your bullet placement. The bullets trajectory is similar to the 30-30, but it is less powerful. The standard weight bullet for the 7.62x39 is around 123 to 125 grains where as the standard bullet weight for the 30-30 is 150 grains. Both move at around 2300 feet per second so the 30-30 is gonna hit harder.
