if you want to test the accuracy according to international standards (ie, competition) you should test it at 25 meters, which is the standard International distance for all pistol competitions, excluding Free pistol and Donald Manson in MLAIC, which is 50 meters.
testing a gun´s accuracy at 7 yards is just wasting time (air pistols are shot at 10 meters in competition) and testing at 15 yards, may fool you, for many reasons:
you wont really see the difference between an average and an accurate gun, too short of a distance. At 25 meters you will be able to see the difference more clearly, as at 15 yards more or less all good guns shoot the same, but at 25 meters an average gun will open far more in groups. You will notice also more clearly the difference between a good sight, ligths, a good trigger, over travel, etc...as 25 meters is not "a forgiving distance", like 15 or 12 yards is.
the target size, at 15 yards IS TWICE AS BIG as the target size at 25 meters...in other words..taking your gun to 25 meters and get accuracy is TWICE AS HARD at shooting at 15 yards.
at 7 yards the target is ridicously big, and anyone can hit a can or steel target as such distances, thought not everybody can do it at the speed of light.
one hand held is more recommended for testing accuracy for two reasons:
you will be more accurate, as your arm is extended, and it is more comfortable, and it is one one hand making mistakes, not two..and you will use only one eye.
a good SAA should be able to hold groups, with selected loads or brands, in the 2" circle, with only some fliers. If you get that level of accuracy, you can compete seriously...if you get less than 2", you have a racing machine.
if you are going to shoot mainly in bullseye, I would stay away from very soft actions, that slow the hammer fall, in the best Cas style. Bullseye shooters dont like and need soft actions, for accuracy, but what they need is a quick hammer fall, with a good trigger job. Thats why Colt, very rightly, stills makes his actions the old way, with stiff hammer springs...for a quick hammer fall that will give you best accuracy with less mistakes.