Here is my load recipe.
Bullet = Sierra 125 grain OTM
Powder = H110 - 18.4 grains (max load for me- some primers flattened)
Primer = CCI #400
Case = 5.56 LC 09 (300 blk specs once fired from Brad's warehouse)
OAL = 2.245 (mag length)
Light crimp (Lee FCD)
As always start 10-15% low and work up to this load. I take no responsibility for the safety of this load.
I don't have any chrono data but it functioned flawlessly and locked the bolt open on an empty magazine. At 50 yards using an Aimpoint micro I was able to shoot just around 1" 5 shot groups. Hope this helps.
My best load with the SMK 125 OTM was over 18.2 grains of H110, using AAC/Remington primed brass from Midway. CAOL 2.125, with a light crimp from a Lee FCD. I wasn't very impressed, not less than 2 MOA out of my 9" AAC upper.
Much better results with the much more expensive Barnes TTSX 130 gr boattail over 18.2 grains of H110, COAL 2.150.