from Ken
However, if you use the size of the round, say 5.56mm and a dispersion factor due to weapon, human, atmospheric and target considerations of about five, that yields a roughly 25mm circular error probable, not 100mm....
Am I positing correctly that this refers to the results at range ?

When I was shooting, I averaged ~1.5" (+/- .25"), 5-shot groups at 100 yds, with an AR-15 (semi-auto) shooting with the std receiver sight and with support (bench, tree stump, mound, etc.). Sid (a Marine sniper before a Bouncer took off his leg) did better with the same rifle, ~1.25" (+/- .25"). My wife on the same weapon was more like 1.75-2.00". So, your 1" groups are very good shooting (would beat Sid). Storr's 100mm (4") was based on what a reasonably well-trained soldier should be able to do at a minimum.

I can't go beyond the range so far as personal experience is concerned. There is such a thing as Match Degradation, where I've managed to go from a practice average off-hand of 85 on international targets down to the 40s. All a long time ago.

Thanks all for the help. Have to see a client now.