100 yds is often considered an acceptable maximum under ideal conditions for the 22LR. That being said, Ive had windy days I couldn't hit a beer can at 75 yrds with any consistancy, and Ive had calm days when I could hit ant hills at 200 yrds lobbing them in there with a S&W 617 (long range sixgunning is so much fun once you get the hang of it, and its not nearly as tough as it sounds, Im no pistol expert by any means). The highpower rifle rounds are another story entirely. Those mentioned, with a trained shooter and under ideal, known conditions are all 1000yd rounds with no struggle. Now at that range they are packing significantly less wallop than at more standard ranges, but lethal none the less. When you get up into the big boomers, cartridges like the 338 Lapua, 408 Chey-Tac, 416 Barret, 300/338 UM and the like, burning b/w 120 and 200 grains of power and pushing 200-300 gr bullets at varmint-class velocities, you can nearly double the above figure. Again, this is all with highly specialized rifles, handloads, and trained, experianced shooters. Alas, a picture is worth a thousand words, you and your son play around with this calculator...

http://www.biggameinfo.com/index.aspx?page=%2fbalcalc.ascx

You can find the pertinant BC of any given bullet on the respective manufacturers web site, which you will need for accurate figures. You'll never know as much as you did when you were 18!!! Having just turned 30 a few days ago, am I but just beginning to figure that out myself ;-)