I have read the original post. And the one I quoted kinda contradicts it; why mention being outmatched at any range with the Jackal?
Not trying to be a smart arse, really; I have no problems when using the jackal in its maximum damage range. Just to make it easier on myself and be extra sure some pellets will not miss I used it for a good amount of time with Aimpoint Enhance. I don't want to be forced to pull up the iron sights against any automatic weapons. This way it remains instinctive play: just frame the head in the reduced circle in semi-auto (NEVER use the auto fire of the Jackal.) and you're in business.
It feels more that instead of the Jackal being your issue is more about the Scar destroying you. Don't worry it's like that with everyone. I rarely manage, in case I need one second shot at my engaging Scar opponent to take him out. While you'll need 1 to 2 shots, 3 if unlucky to take him down, every extra shot the Scar will be punishing you.
Just relax, take the Reflex Sight off, take the Extended Mag off as well. The Jackal is just awesome if you keep its mobility at its top and as long as you use SEMI-AUTO. In fact I'm often surprised when I have no choice but to shoot someone that had the jump on me at an unproper range with the Jackal in hand: "fack quick switch pisto--- meh f*** it." shoot and aim the head regardless, sometimes they still go down. The Jackal sincerely surprises me with its effectiveness.
I don't wanna look like I'm trying to lecture you or systematically contradict you with how you feel about the Jackal but really man, the gun is fine. Marshall feels on the other hand a little random because the cone has a bigger spread than the Jackal in semi-automatic, even if using Aimpoint Enhance and not respectively Oo
I don't use the reflex, and I never take a shot from more than about 5 yards. It's underpowered.