I'll throw my 2 cents in FWIW.

First of both the .243 Winand the .270 Winwill get the job done on TX deer out to 300yds. Both shoot plenty flat enough out to 300yds. With the .243 shot placement is more critical and the .270 packs more FPE, oomph, thump, smack, knock down power or what ever you want to call it. If given a choice between the two, I'd opt for the .270 Win. Remember this,a round that will kill cleanly at long range will also kill cleanly at short range, buta round thatwillcleanly kill atshort range will not neccessarily kill cleanly at long range.

Second, if you are new to shooting and hunting,you would be better off to refrain from attempting 300yds shots or anything remotely approaching 300yds. I would concentrate my shooting both target and hunting at 100ys and no more than 200yds for the near future, until you get some experience under your belt. Shooting 300ydsoff a bench is challenging enough for most experienced shooters and hunters. In the field the difficultly factor is at leastdouble. Withthat said don't be afraid to start shooting out to 300yds once you got 100yds, then200yds fairly well mastered. Don't just shoot off the bench either. Shoot from the standing off hand (at 100yd), kneeling, sitting, and prone positions as well, since more than likely you will not have a bench to shoot off of in the field.

Finally, shoot as often as you can. Don't worry about the quanity of rounds sent down range, instead concentrate on the quality of shots sent down range. Concentrate on the fundamentals. Only perfect practice will result ingood marksmanship. Bad fundamentals will only result in poor habits and poor marksmanship. You will get more out of 20 rounds ofproper execution ofmarksmanship fundamentals, than you will out of 200 rounds just sent down range halfassed.

Once you have somewhat mastered the fundamentals, you will have the knowledge and confidence not only in your rifle, but in yourself to make that shot, regardless of whether it's at 75yds or 300yds.