I can't vouch for the 124 and 137's specifically, but TAC has been fantastic in my 18" 308 with 130 TTSX and 151 absolutes and while it's a bit early, 152 hunters are looking real promising. TAC gives me great velocities and consistent velocity without much trouble. The ball powder fits into that undersized 308 case real well without compression and burns consistently enough I haven't bothered with crimping.
Best thing about TAC: it seems to be among the most available powders right now.
So Tac and 8208 seem to be the preferred powders. Where do I start? Do I run a ladder with each and see what works best? I want to load the 124 and 137 hammer hunters. I have Lapua brass and CCI 200 primers (all I can find these days). Or should I start with one bullet and focus on that until it is dialed in?
Just to keep this thread interesting, I also shot H4895, Varget, Benchmark and CFE223 under the 124HH bullet. They all worked to some degree but compression was the biggest problem. The .308 case just didn't have enough volume to avoid compression while still attaining the velocity I was looking for.
I don't have TAC on hand but it sounds like it may be the best fit by volume. I'd be very interested in hearing the results that others have with TAC & the 124HH. Brass, primers, oal, crimp; the whole 9 yards.
N540, AA2520, or 2000MR might be the other options. I shot N540 in the 06 launching the 137s 3355. Have a couple of boxes of 124s for the 308. Will start with 2000MR using the Remington small rifle primer pocket brass they offered many years ago. They have more case capacity than any brass out there.
Problem with tac is its temp stability...I use it in plinking loads for my 223 and the velocity , SD, and ES can varry quite a bit from 20 degrees to 90 degrees - common hunting temps here in CO depending on the season . It does meter well though- why I use it for bulk plinking ammo.
Gotta make sure you use a chrony with tac, I found that the book velocities are over inflated on what I've been able to achieve in my rifles.