Tamed a 125 on official using primitive mek with cannon shell. 1st shot 1 bullet from tek rifle to get it to aim straight for me. Hop on mek, activate the cannon and aim straight at the head. 99.9 taming efficiency.

Ignore all these others as I've just done it 5 minutes ago. Used a bloodstalker to get in range 1st. Very easy . Solid headshot will knock even a high level out.