I have been doing a ton of shooting lately in the 1000 yard range. I highly recomend atleast 20" x 20". also, it costs alot but if you start with ar-500 or ar-400 (both have worked great for us) you will not regret it. in the last two months we have fired over 600 rounds into these with 338 rum, 338 edge and 300 ultras and they still look like new. In our group we have several circle targets in the 12" to 15" range, and only two that are 18 X 18". the two bigger ones are the ones we set up most often past 800 yards. Wind is the reason. lots of times at 1000 we will make a first round hits (but often on or towards the edge) because of the wind. on the smaller targets it would be a miss. with a hit we can calculate our error and adjust and learn from this. with a miss although the spotter can usually tell where it hit, it can be difficult, especially if the background is any distance beyond a couple of feet behind the target. we still aim small for the center of the plate, but if we are say 8 inches from center because of the wind or... its still nice to have a hit on the steel. just my opinion.
also, on the steel painted white, hits are visable through the scope at 1000 yards. at 1450 yds had to strain to see them, but with the spotting scope (45 power), no problem
