Got my 16" barrel in, got the upper together, should be finished tomorrow as I've been waiting on the gas tube.
I managed to scrounge enough AA1680 from a friend to make about 25 test rounds using 30.0 grs. I'm giving Sierra 125 TMK's, 125gr Hornady SST's, and Nosler 125 BT's a try. If any of those shoot well... 1.5" +/- I'll be needing AA1680.
I do have several pounds of AA2220 if anyone has a recommended load... I had been using W-296 in my .30HRT and if the AA1680 does not work, which I see no reason why it won't, I might play with that powder as well.
Below are the test rounds. Started with virgin Hornady brass, sized in a Hornady Custom Grade 30 Herrett die, as recommended I sized until they just would chamber... using a Hornady comparator and #30 insert, I'm at 2.314". Trimmed to the recommended length of 1.570" and rechecked. Didn't take too much work to get things set up... size/measure, trim, resize/remeasure, chamber in rifle. At 2.314" an occasional piece of brass would stick, but not to the point I had to beat the CH to get it out. So if I'm looking at this right, I'm right at the limit. Will measure fired rounds to see what's the end result and go from there.
I loaded A LOT of rounds for the .30HRT doing the same thing... never had a split neck even after multiple loads, hope I don't have that problem with this barrel the other poster had.