Farrows mutation "Gunslinger" is broken?

Hi, I bumped into this problem on Stalker Trials in The Forbidden City whilst grinding for that nr 1 spot. Coulndn’t do it and maybe because of the second Gunslinger on Farrow didnt go of as intended by only fireing 1 shot after reloding. I tried the same method over and over with the same result, only shooting 1 target. I used the first Gunslinger to kill 2 , hit 1 and miss 1 (using the Elysium). I made a gif showing the problem. However I cant upload it since I am new to the forum. Hope this link works. I have the video of the whole run if needed. Take care.