I coat the bullet with HBN not the bore.
If I'm flirting with pressure signs with my load because I'm chasing the higher velocity node, I can usually reach that desired higher velocity node without the subsequent pressure signs with coated HBN bullets.
Yes, you need to up the charge to regain the velocity, however, in my experience it seems as though chamber pressure drops more than the subsequent drop in velocity with HBN coated bullets. Note: I have no way of actually measuring this other than just using the common signs of a hot load (sticky bolt, cratered primer, ejector marks, etc.).
To me it makes more sense to think of it as a tool, ingredient, or method to take the pressure off your hot loads rather than having to accept a (much) lower but safer velocity node.
I don't bother with HBN otherwise.
Have seen the same with 144 gn Berger Hybrids in 6.5 CM, MPA BA comp rifle, 26”. I needed 0.6 gn of additional H4350 to regain the prior uncoated speed (where the “lower” node is). But now the case neck and most of the shoulder were both covered in soot. Sign of lower than adequate pressure to seal off the case against the chamber. Some kernels got in there and left dents in a few of the case walls. Primers are very rounded, looks like a starting load.
Have not yet pushed this load to its new max. Might go look for the higher node at some point.
Have developed an optimized RL-17 load (not my favorite powder, too temp sensitive, but it is what i have). This was for the Barnes 145 Matchburner bullet: I hit sticky bolt lift at 3020 fps, an eye watering speed for such a heavy bullet, even from a 26” barrel, but this was clearly over-pressure: Lapua case heads expanded 0.2 thou in one firing (micrometer measurement). Case life would have been 2-3 reloads max. So backed way off, and found a nice wide node at 2910 fps, primers now have rounded edges, no cratering, no hard bolt lift, so zero pressure signs. But note that it is an old barrel (2,000 rounds) with lands that have moved forward a lot. So more chamber volume by the time the bullet comes to a stop in the grooves.
IMHO, HBN is fairly easy to do, compared to Moly. But it has pros and cons, and is not for everybody:
Negatives:
1) Load data in the books become fairly useless to you. You have to write your own book.
2) You have to put more powder into the case, and if the case fill is already over 90 or 95%, you either end up with a compressed load, which is not ideal, or it just won’t fit and then you are forced to try a different powder. I managed to stay with the same powders so far, but i have to settle them with an ultrasonic tooth brush before seating. You still hear a tiny crunch.
3) You have to be meticulous in how you coat the bullets, or they come out looking different, and speed can then move by 10-15 fps and push you out of the node.
4) Don’t mix bullets from different coating batches, or SD can double. See point 3 for the reasons why.
5) Don’t forget your coated bullets in the bottle, they will rust/corrode, due to the anti copper fouling agent in the Tubb HBN mix. That is probably where the ammonia smell comes from when you open the bottle.
6) Once a gun has been seasoned, which takes 20-40 rounds, you try to avoid cleaning it too often. Which in practice means all bullets you want to run in that gun now need to be coated. You have to commit. Yes you can give up and clean out the HBN, but you can’t switch every week. Takes too many rounds to season a barrel.
7) You will likely use 4-6% more powder than before, so a slight cost increase.
8) Is barrel life better or worse? Who knows! Pressure can be lower, but you are burning slightly more powder than before. I really don’t know the answer to that.
Upside is:
1) You get the same/similar cold bore speed and point of impact, the hole is usually “in the group”. But not always, just more frequently than before. Useful for hunting applications.
2) You can get more speed if you push up the powder load, or you can aim for same speed at lower pressure. Sometimes this allows you to run at a higher node. Maybe you can gain 100-120 fps this way, but it is not always practical. If you use a double base powder known for speed, you can get some pretty impressive numbers. Bragging rights. But speed is over-rated, and at best wind drift will come down 5% or so.
I use it in my MPA target rifle only. In that gun, a 6.5 CM almost achieves 6.5x284 performance.
