However, the ONLY way to test loads for accuracy is to remove all shooter-related error possible and that means a bench and sandbags.
CraigC, yes I agree with you about determining "mechanical" accuracy and stated on post #14,
"I believe shooting from rest/sand bags will test "absolute technical" accuracy, but not actual practical/tactical shooting accuracy. The pure empirical accuracy attained from rest/sand bag shooting is nice to show to your friends, but it's shot groups off hand (my hands) that will impress me."
But the ONLY way to test how your loads will shoot out of your pistol/hands is to shoot them off hand, which I believe is more pertinent. Even though you determined the "mechanical" accuracy of your pistol, you will most likely end up shooting your pistol off hand most of the times for plinking, range practice, match shooting and SD/HD training.
When I first started match shooting 15 years ago, I used to test my shot groups from sand bags at 15/25 yards. With my 1911, I got 1.25" average shot groups at 25 yards. Of course, my off hand shot groups were much larger.
The shooting/reloading mentor who taught me stated the "mechanical" accuracy of a pistol is nice to know, but won't give you reliable shooting data (SD/HD/match shooting) until you get consistent off hand shot groups (he shot Bullseye/USPSA).
I agree that user input will add variables to the testing of shot groups. This is what I do to address that. I first start at 5 yards and slow/deliberate shots usually produce a single hole or sub 1" shot groups (if I don't, I investigate the cause). Then I incrementally move the target to 7, 10, 15 yards, but
only after I am able to produce consistent tight shot groups. This process not only tests the functional accuracy of the load/pistol combination but also "force train" the shooter to continuously eliminate the variables and shoot more consistently as if shot groups are erratic, the causes are investigated (pulling/jerking trigger, etc.). Holes on target don't lie - they reveal what you are doing wrong.
Many shooters tell me they bought their pistols because of certain published shot groups that were particularly small with a certain ammunition (either from ransom rest or pistol rest/sand bags). But I ask them, "How does it shoot in your hands with your choice of ammunition?"