Additionally, providing you hit the target, the bullet must retain the ability to do sufficient work to secure the game, especially at distance. At 1000 yards the STW gives full penetration on an antelope, I'm not sure the same could be said for the .243 Win..
I believe some time back, there was video of a young gal shooting an elk at about 1000 yards with a.243 and it was a 1 shot kill. Fluke? Maybe. Would I recommend it? No. However,I guess it does happen
