Kinetic Gem : Muh Keen Gun NOT WORKING

[大勾勾]

I always got feeling about there are something missing when I playing Sniper, So I tried in DEMO mode find kinetic gem on Muh Keen Gun is not working. I remember when Sniper use Assassinate, it changes animation.
already unload Full-Bore Bonanza but now there is no different.
And here some info:
WEAPON : Inscribed Muh Keen Gun --> loaded 2 inscribed gem (Assassination kills & Shrapnel Tower Damage) 1 kinetic gem (Muh Keen Gun)
Head & Shoulder & Arms are normal rare set (no animation change)
Back : Full-Bore Bonanza (which change animation of headshot)