Well up until about this time last year, this was basically my situation. I have hunted using similar rifles most of my life. In and around 10 years ago, my daughter and I built our own range here on our farm. We painfully measured the yardages out to 300 yards using a 100ft tape. I developed loads through the years ro optimum performance out to 400yds, and after having the range to check the loads it was very much a learning experience. Just about all of the loads shot as predicted and were well within MOA out to the 300yd target. This only validated what I had hoped and worked for when working up the loads.
After this, I knew what the actual drops were on my loads and then my ranges were extended to a little further than what I had previously shot. I did as most and started off on varmints such as yotes and our booming feral hog population. This gave me the confidence in my, and the rifles abilities to shoot my first 400yd whitetail.
When shooting the plex, you can use them for measureing and some ranging just as easily as the mil dots and such, to a certian degree. You do have to check them at set powers and known ranges however to know, "hey I am getting the bottom half of the plex on a brisket to back, and that should be 300yds according to what I measured off."
I used several things to check out our different scopes but the best was a t-post that we painted of in 6" increments. The post could be easily moved and quickly set up at the various ranges. The marks were contrasting black and white, so that you could judge the differences closly on the reticle.
IT isn't as precise as what I am doing now, but then again, at the time, I never imagined having something that does, nor shooting at anything consistantly over 400yds. It will however give you the knowledge to use a standard plex scope to range and shoot confidently to further distances.
I know that my 25-05 using my handload, will drop around 18" at 400 yds on average, from a 200yd zero. The Leupold that I had on it, could be used to judge, the brisket to back on a whitetail which is on average about that same distance. Then it was simply account for the breeze if there was any and slip on into the vitals. For deer this was about the furtherest I would shoot.
