Honestly you're just wasting time NOT getting a laser rangefinder (or at least borrowing one from someone who has an extra you can borrow or "rent" for the year). The reason I say that is they are THE greatest learning tool you can have for learning how to estimate range. With only a few weeks of frequent use you'll be surprised how good you can get at estimating different objects at range. And I mean just that, don't worry about ranging animals, instead range rocks, fenceposts, unique trees, old stands, barns etc... ANYTHING that jumps out at you and is fairly easy to get a sense of scale with by looking at. (Trying to get a sense of scale and judging range while lying down or in very steep terrain is super tough.)

After awhile you'll be able to get pretty close (within 50 or so yds) all the way to distances as far as 400yds in open terrain. After that it gets awfully difficult unless you have some point of reference like a fence or powerline with known distances between sections/posts.

Good luck,
HL