Accuracy and killing efficiency at long range is conditioned by two thing's. One is the quality of equipment, and the other is the ability of the shooter. I have witnessed some long range events where shooter's were shooting with long range Gibbs and Whitworth rifle's. You would not believe what these guy's can do. To them 300 yards is a short distance.
300 yards to an experienced rifleman with the proper equipment is not a problem. All it takes is practice, and a little money to buy the proper equipment.
I am by no means a ballistic expert, but I imagine a 525 grain conical at 1600-1800 fps can kill deer a long way out. Remember energy is not everything. If energy was the only factor then how could a buffalo hunter kill a buffalo at 1,000 yards??And yes the trajectory would be a rainbow, but there are guy's who do it everyday.
I shoot BP in my Sharp's rifle in 45-70 with a 405 grain cast bullet. I am extremely confident in my killing ability to 200 yards. I have been practicing to 400 yards-but I would not attempt that shot. Hopefully by this deer season I will be confident out to 250 or 300 yards. Tom.
In this picture you are looking at $2500 worth of equipment. Long distance shooting is expensive.