I thought I could trick my BLK into acting more like his 308 big brother, since i'm using a "long" 16" barrel I could use slower powder and get more velocity with less relative pressure. The sierra 125 SP is the lightest bullet that seem to shoot well AND be constructed tough enough for my purposes of deer/hog hunting, so ALL TESTS were done with this bullet. My thought being trying to get enough velocity to acheive bullet performance/expansion out to my effective offhand hunting distance of about 200 yards, and have 1000 ft/lbs of energy, this made my target velocity 2500 fps.
I tried IMR 4227, IMR 4198, Reloader 7, and BL-C(2) which are all a few places progressively slower down the burn rate chart I use (http://www.reloadbench.com/burn.html
) I tried each from a starting load incrimentally up to a compressed load, and got worse and worse results as I tried the next slowest power. (Silly I tried that many, I know, but I wanted BL-C(2) to work SOO badly because it is so awesome in my 308 and 223, meters so well, is clean, and CHEAP!)
IMR 4227 at least burned all the power, but gave a top velocity of ~1700fps, with only moderatly horrible extreme spread.
IMR 4198 left some unburnt powder residue, top velocity was ~1400fps, didnt bother to shoot more than one.
Reloader 7 did ok at lower charge densities (when the case was about 2/3rds full), but peak velocity was ~1600fps and got lower as I approached 100% case capacity, also didnt burn the entire charge.
My beloved BL-C(2) did horribly. It gave a top velocity of ~1100fps, and left tons of unburnt powder/residue all thru the gun.
So my half day for experimentation ended up being more of a "What DOESNT work" list of slower powders. I tried a couple of faster powders just because I had them and I had the chrony all set up, but didnt find anything that worked better than Lil'Gun (best extreme spread EVER!) or H110 (best velocity I've gotten out of my BLK so far)
Alliant 2400 gave me a top velocity of 2398 fps right around 100% load density, but my temporary excitement abated when upon loading a string of 10 the average fps was 2240, with a REALLY high extreme spread.
So I agree with JohnInNH and agBQ08, the best for 110/125g bullets for accuracy/low extreme spreads is Lil'Gun (my best load is 2100 fps with a 15 fps extreme spread, and velocity tops out at 2200 fps), and H110 will get you a little more velocity with not quite as good of extreme spreads and its a bit dirtier. (my velocity topped out at 2300 fps, with 2200 fps being my accurite load with about 40 fps extreme spread)