I've been using hBN since it became available and at that time there was but one source. I think it was the spring of '13. Then there were many different ways of applying hBN to bullets and barrels with equal differing results. I'm uncomfortable second-handing others reports so I'll give my experiences only. I use a clear plastic relish jar half filled with corn media with a teaspoon of hBN powder (first use only, thereafter .25 that amount each batch). My usual load is 25 338 256-285 gr solids or the same number of 270 bullets (only to simplify as more could be added). Usually I run two jars as that seems to balance out the tumbler. I then tumble for a minimum of two hours and have gone as long as five hours; seems to make little difference after the initial two. Remove, inspect, and rack these processed projectiles. They are ready to load. I do not polish them.
The barrel treatment is different. I use 99% isopropyl alcohol (16 oz.) to 1/8 cup of hBN. With a new barrel I'll fire 18-21 rounds before treating. THOROUGHLY CLEAN, then run a soaked swab or patch through six times. Because it's convenient I let the barrel "cure" overnight after removing any excess from the brake or chamber/action leak. I make every effort to keep the chamber hBN free.
First group (three rounds) indicate higher pressure (bolt cycle), but reduced velocity. Those traits disappear within the following two groups. After that I experience no cold shots. I couldn't say if velocity is increased or decreased as I haven't shot either bullets or barrels minus the hBN treatment since mid '13. Cleaning is generally easier and never harder; patch residue changes with powder/bullet changes as expected. Accuracy has improved, but I think that's me and I cannot verify specific results isolated from non-use of hBN. I doubt I'll ever use untreated bullets and barrels again.
This keyboard is both skipping and doubling so my apologies if there's any typos I missed correcting.
Here's some photos that may help: