Ended up chopping a 22" Lite SS to 18", threaded 1/2-28 with a cheapo Amazon adapter. Hornady brass with 5+ firings, blem 107 SMK, 43 grains of 7828SSC. Average 2750 over 10 shots at very low pressure. This was the same load a 20" 243 Improved shot at 2800 fps fully broken in.
The two outside the group were 13 rounds in to the shot string on a dead calm day, so mirage was getting bad. Looks like it should be a good barrel.
Once the barrel has 100 rounds of this training load through it, 116 TMKs will get speed tested with SB65, RL16, N560 and H1000.