There are two kinds of accuracy in question here. First: which loads work well with a particular gun, and second: the practical shooting accuracy of a particular gun, load, and shooter interface.
When working up loads for one of my hand guns, I look for combinations that are substantially less than 2" at 25 yds. While I occasionally shoot beyond that distance, 25 yds generally tells me what I need to know. If I acquire a piece that will not beat the 2" standard at 25, I find another home for it. The only exceptions to that rule are my wife's and my carry pieces...both snubbies and these come very close...less than 3" at the same distance.
Testing loads and guns is done from a sitting position with my back rested against a porch post. The gun is extended out between my upraised knees and fired with both hands gripping. I've found that this position (really Keith's old long range position) is as good as shooting off bags for me and allows me to zero the gun for field shooting at the same time.
Practical shooting is something else. I can hold 2+" at 25 yds. on most days, shooting offhand with a good Weaver two hand grip. I'm 64 now and I need clean glasses and must be having a good "eyes" day. For slow fire, offhand work, I need well blackened sights, no wind, and the sun behind me to do my best work. This is what I term field shooting and applies to deer hunting or pretty much any other recreational shooting. Out at about 80 yds from our porch here on the farm is an old 20# propane tank which offers a good offhand target...I can keep a cylinder full or a full magazine from one of my 1911's on it shooting in a rapid fire cadence. From sitting, a railroad tie plate (8x15") makes a good target at 100 yds, and I'm nearly as successful.
For CCW defensive shooting, the grouping depends on the range and speed required. We practice here at 3 to 10 yds, shooting double taps for the most part, and all double action. My wife and I carry S&W's...her's a .38 Spl +P Airweight 637, and mine; a M-36 with a 3" bbl. Double action it's no trick for either of us to keep a double tap at 3" or less from 10 yds, taking a little time to get it right. Up close at 3 yds or less, shooting at speed and from the leather, for the most part, all of our shots will stay on an 8" paper plate.
HTH's Rodfac