After you use them a while you usually end up with some that don't work and that is what I use for practice. I have also heard of people using different size set screws screwed into the bottom of the nock to make the nock weight even - either way should work
I have a couple I've killed deer with that no longer work. I shoot those when I BH tune just to verify.
For my other arrows I cut a piece of insulated wire and super glue it into the BH then use a grain scale to get the ~25 grains or whatever the weight is. Insulated NM wire fits perfect.
To be honest, POI (at least for someone who shoots like I do) is hardly noticeable but I like projects...
Last season I found an arrow in the dark 6 days after I shot a deer with it. Decided to leave it on and see how long I could see it in my basement. Well over a month and it was still on. I got tired of looking at it. These were cheap imitation nocturnals.
I superglued pieces of 6-32 threaded steel rod inside my 0.204" Bohning A Nocks to simulate the weight of Firenocks. 6-32 steel rod weighs approximately 21 grains per inch and fits nicely inside these nocks. 8-32 rod fits better in 0.246" nocks.
I cut open a #7 1/2 shotgun shell and glued the lead pellets in the nock until I reached the weight I needed. The pellets fit a little loose and drop down inside nicely. If you need more weight then you can fit in the nock, just smash them down a little bit and then stack the little disks in and glue.