I'll address your last statement first: You aren't sure whether the guns even need lapping. They do. I haven't heard of a rifled barrel yet that didn't benifit from lapping. They are all made by machines and men, bot subject to imperfections. Lapping removes the errors and imperfections.
Since all barrels are individuals, the amount of lapping required will vary with each. Use a push through slug before lapping and you WILL KNOW the barrel needs smoothing. Fire maybe 15 or 20 shots, clean the barrel till most of the lap residue is gone and try another push through. Continue lapping if there is any variation in pressure required to move a push through from breech to muzzle.
Lap bullet can be fired in either direction without getting the job done bass ackward.
Bullseye is an excellent powder. For the large case start with 3 grains and if a bullet sticks in the barrel, remove it as the lap instructions describe how to, and up the charge a little. If your first shot barely makes it, so you can see it in flight and it is dropping like an old Daisy fired BB in flight, up the charge a half grain. Lap compound builds up in the bore slightly with the first 5 shots or so, making the push required to get them out the barrel a little greater with each shot. After 5 shots or so, your bullets speed and trajectory will be very uniform, enough so that you can print real tight groups at close range. - A little story about lap bullet accuracy. A customer told me he was lapping a 44 or 45 revolver and accuracy was so tight he was clipping frozen twigs from an apple tree in the yard. When a starling landed in the top of the tree, he sent his next lap shot for the center of it's behind. He said the bird saw the bullet coming and swung its head to see what it was, but couldn't react fast enough to get out of the way. The 300 gr bullet, flying so slow it was clearly visable in flight, went through through the bird dead center, then became visable again as it exited and went on.
For those wanting to lap a 22 rimfire, I find the easiest way to know when one is done is to fire five shot groups at 25 yards, with lap charged bullets, until group size quits shrinking. When you've fired two groups with all shots going through one hole, just switch to clean ammo and let it clean the barrel of any lap residue. After a few clean bullets have gone through its a good idea to clean any lap residue fromt the action.
