i am wondering what caliber would be best for shooting 400-1000 yards. i have heard everything from .243 to .260 to .270 and of course .308. i am on a budget and reloading isn't an option as of now... i want to go with a bi-pod and was wondering the best manufacturer. also is it preferred to have a detachable box mag? i have looked @ savage and Remington and i'm leaning towards the latter....any help would be great