All this stuff about "lapping" is just hooey,
There's no need for it, your barrel is and will be fine without it.
You put a twist on your question by adding "before sighting in".
Here's the real deal,
You'll be shooting it with whatever load you choose to begin with right?
So start with a large paper and kinda close like 25yrds,
Shoot for group with the very first 5 shot's,
Adjust the sights for center, and shoot some more.
Now what should happen, is you'll be experimenting with the powder charge adjusting up and down in 5grn increments looking for a tighter group, Then you'll be experimenting with the amount of lube you use on the patch,, Looking for a tighter group,, Then you can experiment with the fabric thickness,, Looking for a tighter group,, You can experiment with all of the above with a different size ball.
All the while Looking for a Tighter group.
You don't have to mess with the sights all the time as this will just screw ya up, your experimenting, changing things, shooting for a tight group not the bullseye. Once you have a consistent one hole group at say 50yrds, then adjust the sights to move that group to center.
During this experimenting process, you'll end up shooting 150-200 rounds and that's about what it takes to get your barrel broke in.
You can skip all this, lap the barrel shoot 50rnds and call it good, but you'll end up with a gun that you don't really know and a load combination that's kind of OK but not a real match winner.
You and the gun are better served if you shoot it and don't use any technique to "speed things along"
Good luck.