Electrical tape teds to peel off and get stuck in the tubes because it's almost impossible to put it in without stretching it.
Get yourself a roll of aluminum foil (real aluminum, not mylar) HVAC tape and you'll be set for life; easy to cut apply and a bit less easy to remove (good thing). You can even layer it if you need to.
Here is the link to Jim White's bushing chart. Gamaliel Shooting Supply sells Hornady bushings that have a part number the same as their inside diameter. Locate the bushing on the chart that you want to go smaller than and order a few Hornady bushings to do the job.
I custom fit all my bushings (for MEC). I fill the hole with bedding epoxy and drill it out with a numbered drill bit to the exact size I want it. If it drops a little light, just drill or sand out the hole a bit. You can get your weight down to the 10th real easy.
it ain't the bushing; it's the powder. densities vary from batch to batch. that's why they don't always throw a true weight per unit volume. makes an adjustable charge bar worth its weight in gold. good luck with it
You CAN file out a bushing but that's iffy. If you go too far you have to find a way to replace what you took out. I don't file anyway...I use a gently-tapered reamer to remove metal a little at a time from the bottom of the bushing. I prefer to start just a bit large and reduce with HVAC tape,,,it's easily undone.
Get a bushing that throws slightly less than you want. Use a reamer and open up the top of the bushing a little and put in press and weigh 5 cycles to get a weight. Keep taking small bites with the reamer until you get the desired drop. Get a felt pen and write the powder and drop on the bushing for further reference. Ceil
Quartering is right. I use both red and green dot powders. Lots vary in weight. I try to purchase at least a years supply at a time. In the past, I too have had variations of 2 grains when changing lots. 40 years ago, a friend made me a set of bushings with graduated sized diameters. They work just great.