Mawgie,
I'm new to this board but an old hand with the Ruger single action. To me it sounds as though you are approaching the process in a well thought out manner and should soon progress in your skills. If I have learned anything about shooting open sighted handguns, I'll try to pass along some of what I have learned.
First, it is very important to shoot with the sights shaded when conducting any kind of accuracy or performance testing. The direction that any light comes from can make a substantial difference to group size and location, so it must be factored in. The rear sights on Ruger handguns can often come with a certain amount of side to side playthat can shift bullet impact especially at longer ranges, so should be looked at right off and shimmed if need be. An aluminum pop can provides an excellent source of material for that purpose, but the rear sight needs to be removed and the shim fitted so as not show. You may need to use more than one layer of shim material depending on the amount of play being taken up. Then check for rear sight function after re-installing to be certain that the rear sight is free to move up and down without sticking or binding.
When shooting for accuracy, I have found that sitting on the ground, leaning back on a "home made" back board, adjustable for recline works better than a bench rest. I hold the handgun in a normal shooting grip and place my hands between my kness with my feet spread to provide an effortless "craddle" to rest the gun hands. Just be careful when shooting this way, not to allow the cylinder gap to be positioned so that escaping gasses can get to your knees because it is not only painfull when that happens, it can cut through your pants and into your skin! If you try this method, dry fire a few times at a distant target to get the "feel" for how to make it work for you and I think that you will like shooting this way for tests and such.
Since you do your own trigger work, I would suggest that if you have not already done so, you should experiment with a trigger stop device and make certain that the trigger breaks clean and crisp and stops just at the instant that it lets go of the hammer. Trigger pull weight is subjective, but I like mine in the range of 2-21/2 pounds with stop.
You may want to touch-up your sights before shooting, using a black sharpie marker to dull any reflective surfaces as that will help you obtain a cleaner sight picture. It isn't perfect, but is effective.
I like to use a generous sized target with a black six inch bull centered and shoot at 50 yards for sight-in and first stage accuracy work. That way any mistakes or problems that I may be having are more pronounced and easier to read and fix. I sight-in 3 inches high at 50 yards with all of my center fire magnum handguns including the .357, but especially with the .41 and .44 magnums. For me, that setting takes best advantage of the cartridge.
I hope that you enjoy your Bisley, they fine handguns.