Re: 300 Rum Vs. 338 Lapua
Yes the 300 RUM can be VERY effective past 1000 yards. Its up to your personal preferance. If using the highest quality brass is most important to you along with a bigger than 308 cal bullet, then the 338 LM is for you. If flatter trajectory is important, go with the 300 RUM.
You cant go wrong with either. They are both awesome 1000+ yard performers.
Long range shooting is a process that ends with a result. Once you start to focus on the result (how bad your last shot was, how big the group is going to be, what your buck will score, what your match score is, what place you are in...) then you loose the capacity to focus on the process.