Milanuk,
Lynn knows his 6BRs as well as anyone on this board, but let me just add a different perspective. My gun with a 3-groove Pac-Nor has shot bugholes at 2720 fps and 2940 fps and many places in between. It has shot bugholes with three different powders, and with bullets seated .022" jam and .010" jump. This is with CCI450s and Varget, IMR 4895, and Norma 203B. Haven't tried H4895 yet, but the IMR Version has a slightly longer pressure curve and QuickLoad predicts it is better for the 6BR.
As to narrow tuning points what I HAVE observed is that very small variations in load and seating depth can make big differences in velocity! I agree with working in 0.2gr increments as you near your pressure max--but mainly so you don't go too hot.
Regarding those load methods, particularly OCW, I don't think you'll find them that useful. The 6BR is so accurate, with so little vertical,with good bullets) that what you really want is low ES/SD for long range. For that, leave the flash holes alone and concentrate on very consistent neck tension. Honestly, I can pretty much load any velocity from min to max and the gun will shoot as well as I can hold-- 0.2 moa for five, high Ones for three.
This target shows three-shot groups with nine different loads,from 30.2 to 30.8) using two different powders,Varget, IMR 4895) and Scenar 105s. Honestly, what little vertical is in there is probably the shooter. And my Norma 203B testing is pretty much the same. Shot well from very light loads to brass-trashing pressures. John Brewer recently tested some Scenar 105s I sent him. He just loaded five into the lands, and five jumped about .012" and both ended up with < 1/2" vertical at 300 yards with his "starting" load.
So, I think with a good barrel, the 6BR may be a lot less fussy than Lynn suggests, though I agree with him 100% that testing at 300 yards may reveal that a .1gr difference may indeed separate a "good" load from a great load.
But it may be overkill to spend a huge amount of time to find the "perfect" load because a 15-degree change in ambient temperatures is going to raise/lower your case pressure by a LOT, even with Varget.
Jim Borden says with a good 6PPC there is about a 100fps accuracy window. I think that concept applies to the 6BR, though it may be more like about 60 fps. And of course that depends on the bullet and the barrel.
Regarding velocity variations there are many reasons for this. Lynn correctly pointed out that Chrons can be inconsistent. Henry Childs did a test with two Oehlers and one shooting Chrony in-line and the Shooting Chrony gave numbers that were > 40 fps higher than the Oehlers.
Then you've got these variables,rough estimates of induced variation):
1. Primer Choice: +/- 25 fps
2. Barrel friction and land configuration: +/- 50-70 fps
3. Moly vs. Naked Bullet: + 30-60 fps
4. Seating depth: +/- 10-60 fps,assuming same charge)
5. Tight bore vs. "open" bore: +/- 50-70 fps
6. Chrony variation: +/- 10-50 fps
7. Short Bearing surface bullet vs. long bearing surface,of same weight): +/- 50 fps
8. Twist rate,1:10 vs 1:8): +/- 20-40 fps
9. Ambient temps and sun vs. shade: +/- 10-60 fps, depending on powder.
Obviously you can see how it is easy to get different max Velocities even with two 6BRs with 28" barrels, and even with the same brand chrons.
What I would do to start, is go .005"-.010" into the lands and find the Varget load that runs about 2850 fps. That should be a very accurate node that yield good brass life. Then work up in 0.2" grain increments and see if your groups shrink with velocity. Monitor the ES/SD along the way.
When you find a load at 2850+ that has good ES/SD, nice tight clusters, low vertical at 300 yards, and VERY IMPORTANT, doesn't abuse the brass, then you're good to go.
Honestly, after 4 weekends of load testing, I've never found anything better than 30.4 Varget, .010" into the lands which was the second "recipe" I tried. But 30.2 Varget jumped .005" shot just as well, with equal ES, as did 30.2 IMR 4895, and 30.3 Norma 203B,the latter two loads jammed .010").
I'm not saying you won't find a "perfect" recipe. But you may find there are a dozen really good recipes that shoot better than you can hold. I have little doubt that when I get around to trying VV N150 and RL15, those powders will probably shoot bugholes as well. And I bet that would apply to you, assuming you've got a good barrel and a good bedding job on that rifle.
There is a reason the 6BR cartridge "owns" the 300m game and that shooters can and do win using factory ammo. The brass is really good, the bullets are really good, and the case runs near 100% load density with many different quality powders. FYI, the factory ammo is running about 2800 with naked bullets: http://www.6mmbr.com/factoryammo.html
Norma uses 203B in their factory ammo. Lapua won't tell us, but I bet it's N540 or N150 or something very similar.
