.243win is a great deer round, 250yrds is getting out there a ways, but in a pinch, the .243 would do just fine, just try not to make a habit of it as your margin of error for placement never changes, but at long ranges, your natural error and human error becomes magnified. If you can put the bullet where it needs to go, and you know it (i.e. actually go out and shoot at 250yrds), and you get good groups, any range you' d feel confident in making a good shot is feasible, most people shouldn' t take shots over 200yrds, some shouldn' t take a shot over P-B range, while others of us can shoot confidently and rightfully so at 600yrds, it' s all in your hands. The .243 will do it just fine for the range you' ve set for yourself, just know where your bullet is going.