Just a quick question of curiosity…
I’m working on my clone load for a Douglas SPR barreled upper. I have a good accuracy load, for the most part. Now I want some velocity. I worked on an OCW load today, and at .2 grains from max, am still only at 2690, using TAC.
I know I’ll get there by max, but I’m just wondering where you guys are with your velocities. Specifically using this barrel. It’s the 1-7, from Centurian Arms by the way.
I use 24.0 of TAC behind 77 SMK. I’m not sure of the exact velocity but it hammers.
I had a guy tell me he was after velocity last weekend… so I suggested TAC based on some of the reports here. He said he thought it was Temp sensitive so he was using RE 15 (possibly the most temp sensitive crap ever made) 
The loads that are getting best velocities are using ball powders.
I don’t use SMKs, but load data should be fairly similar to Nosler 77 custom comps. Nosler data for TAC gives 23.5gr as the max load, and a velocity of 2658 out of a 20" barrel. If you’re at 2690 with an 18" barrel, I wouldn’t push it much further unless you’re being really observant for pressure signs.
I typically use 22.9gr TAC behind my 77s, and average 2540 fps out of a Noveske 18" SPR barrel. This is pretty much spot-on for Nosler’s posted data.
I’m at 24.7gr TAC, 77SMK, FGMM primer, virgin LC, 2.245" OAL, LFCD. This is a 5.56 pressure load, so work up. It’s an absolute hammer. Velocity is over 2700 in 18" DD CHF barrel.
Mk262 is loaded at the upper end of 5.56 pressures. It is a very hot load! The data you are looking at is most likely 223 Rem, not 5.56, which explains the velocity deficiency.
TAC can get you to Mk262 velocities, but it is NOT recommended to go beyond industry recommended load data and SAAMI pressures unless you really know what you are doing. You will very likely start popping primers and you will definitely get decreased brass life.
I’m using Nosler 77 Custom Comps, with 24.3gr TAC I’m at 2690. I want to get to 2700 and Ramshot lists 24.8 as a max in a NATO chamber. I’m not worried about case life, these will be loaded and put away. I’ll be using a separate load for practice and target shooting.
MV for my load above is 2701 from DD 18" CHF/S2W barrel. SD = 31 with a Chrony Beta garbage chronograph.