My situation arose the other week when I set out to load some accubonds in my .270 win hunting rifle. I had decided to change from Bergers. Anyway, the bullets seated extremely hard, leaving a seating stem mark. There were a couple bullets I ended up pulling, and I could not believe how hard it was to pull them, or how many hard wacks it took with my kinetic puller. I decided to buy some new Norma brass. That brass came in, and no joy testing it recently. I've shot with hBN for years now too. I started cleaning with STM and noticed harder seating, and read of accounts of this so blamed it on my cleaning methods for the most part here until recently. I'm also trying out some different Hornday A-max loads in my AR and those were seating kinda hard to the point I bedded my seating stem. Problem solved on bullet deformation. Cool trick. But they are still hard to pull. My 6xc match loads seat pretty nice, but you can still feel the rougher seat (have never really paid much attention to it, til now), and upon pulling all of these bullets the vertical striatations cut into the bullet were evident. This all came to a head tonight when loading bare bullets for a friends .300 WSM and noticing that they seated like butter, and pulled like butter, with no striations/grooving. This lead me to do multiple informal tests.
My coated 200 AB's for another rifle seated rough in his .300 WSM brass that I cleaned with STM. This is the same brass that left absolutely no marks on the bare NAB bullets. All brass trimmed and chamfered with a Giraud. The only bullets I don't coat are my 115 DTACs from SSS, so I used these as a control figuring they were coated better than myself. Never really had a problem seating them, but you can feel the roughness in comparison to bare bullets. I've read hBN is really best as a lubricant when used against itself. I burnish all of my bores with a alcohol and hBN solution for this reason. Anyway, the DTACs show striations as well. My .223 stuff shows grooving too, and I've got some 80 smk's and a-maxes that I know coated very nicely (dull and slick). I had some left over molied Bergers that I tested in my new Norma .270 brass, smooth in, smooth out, no grooves. I burnished a neck with hBN thinking hBN on hBN might help....it did not. I then took a bare bullet and seated it into this brass that had been burnished with hBN, and it was tough to pull and came out with the grooves. I took an fired 6xc case, wiped the outside, sized, and expanded it, and seated a bullet. Very nice, and it was obvious the carbon protected the bullet upon pulling it. Barely noticeable striations, but not grooved. I then did the same test but this time brushed the neck with a nylon brush to mimic some cleaning such as just corn cob. Pretty good, but some slight grooving upon pulling it.
I've been shooting hBN for a number of years now. I have 6xc loads that shoot good, but I never knew how much more extra grip the bullets were getting, really more so in some of my other cartridges. Last week's findings made me think I needed to start annealing, which I'm not opposed to because I'm on a kick of restoring brass to like new and keeping tension consistent, but as one can see there are a lot of variables at play here. My .270 win load development was poor, and now maybe I know why! I love the infrequent cleaning I do on my barrels, but the grip on some of these bullets is unreal. Lately I have been coating with just different caliber bullets cleaned in rubbing alcohol, that have been preheated before tumbling 1.5+ hours. My old method I would clean, and tumble with BB's for 4 hours. The only bullets that had very subtle grooving were some 175 SMK's that I've had a long time and were tested in my friend's 300 wsm cases. They seated and pulled pretty nicely.
These are my informal observations of late. My only theory right now is that longer tumbling with a media like BB's might be necessary to help lay down those hard angular particles of hBN down nice and flat and smooth. That, and don't get the necks perfectly clean. Not sure how to handle new brass, or if the first mentioned theory will mitigate the problem on new brass all together. I apologize if this post is a bit disorganized.
-Conrad