Interesting load, I admit it sure never occurred to me to stray far from Varget burn rates, with 107 grain class bullets.
I could definitely see running 4350 with the 6mm “heavies” if one had the barrel twist for them, given the proportions of the BR case are conducive to fast combustion.
I’m rediscovering .243’s lately as a result of what powders I have and need to use, and general bullet unavailability. In that regard I’m saddened that the original 115 DTAC is off the market, although I do have some on hand.
In that longer columned case, I can run slower power, at higher volumes, but I don’t think I get more speed or accuracy than RE 17, at say 40.0 with 115, coated. That load I put down a decade ago when my .284’s got running, and am only now revisiting it.
I can only say, again, it’s a shame those HBN bullets aren’t available, nor as bare. The 110 ATips are out there, but those are only very slightly less expensive than for example, the 300 .338 A-Tip, which I have difficulty reconciling out of principle.
I would not have ever built a 6BR with the 1-8 twist on purpose, I favre the 1-10 for the reasons you stated. I always thought it was just meant for the 80 grain and lighter bullets, which is hiow I always ran.
But this summer I built a new 6mm Remington Ackley improved to make reliable hit's on small varmint, ground hogs and smaller, to the occasional yote. But after thinking I could drive these big 105 to 108 at 3300 fps and do it with the accuracy these guy's are using them to shoot 600 and 1000 yards breaking records with them, I slipped up on one fact!
After starting the project I called Randy Robinett to order some of his 104's for this project. At that time he imeadiatly said " I really hate to sell you them for that gun"? His next remark was I just assure you they will stay together at those "RPM's"!
This threw me thinking they are proven in a 1-8 twist, and yours are some of the best. Then he explained the extra heat from the speed, as well as how revaluations per minute, are a more meaningful measure of what they will take than the revolutions' per inch!
After a coupkle pounds of H4831sc and IMR 7828 two things became obvious.
1) I had no problem getting these 108 EH out the barrel at 3300 fps with change.
2) They liked right around that 3000 fps mark before groups started opening up!
So, not being a dasher fan,, and my smith not having a BRA reamer,, we cut the 28" .236" 4 grove Krieger that spent the money to have Kathy at 300 Cryo Plus to freeze for me, to a 26" and see what the 6BR would do for accuracy, planning on 2800 fps being doable!
Then after scouring and reading the very limited posts on using H4350 in this case. Seeing how everyone said they had less than stelar results, and not being able to get enough in the case, I had to try myself and fill in the missing why it won't work!
First thing seemed obvious, once UI found a time intensive way of getting 34.5 grains to fill just to the bottom of the neck, I had to be safe, because you can't get enough in the case to hit max??????????????
First shot looked good, a little low of my 95 grain and Varget zero, then the second shot, as soon as I fired it I smelled that odor and said dam you just blancked a primer! Sure enough I did, but on the Custom Axis action the bolt lift was light? so I continued. Then two shots and the hole is just getting a little bigger, with the last two shots blaking and each tearing just a little lower enlarging that hole.
It was late and cloudy, no wind but without the chrony I was like,,, well will this work or not. So next day rain, but very light wind, I couldn't stand it, so Back to the range, and between sprinkles I managed on chono reading without the ERR1 reading, the 2896 fps I said hell ya, but still don't know the spread I will be working with.
But wth light bolt lift, and this being a great powder for the 26" barrel, I am thrilled to continue to work with it. I have a few 5 shot loads ready to test when weather permits.
Anyway I think I know why all the glory these bullets get now are between 2800 and 3050 fps. And why use a 6 AI to drive them 3000 when this little BR likes to do it at 2900 fps? I'll have a new 1-10" twist here soon to build the 6x47L on to take the place of the AI, I just think running 65-80 grain bullets is a poor choice for any varmint at over 600 yards, so the 6x47L is appealing and probably see what I can get out of 95 grain Bibbs for my over 600 varmint needs? If nothing else, I'll have a great barrel for my next 6BR Norma when my reincarnated Pence 1-10 barrel sees it end!
