Re: Westcliff Shooting Range.
A crossbow seems like a bad idea. I used a pistol that could be shot 3 times before reloading. That way if I missed by a fraction of an inch I could adjust slightly and shoot again without waiting to reload. Aim for the heads too. What I did I just chose a small area and get every one in that area because they pop up so quickly it doesn't make sense to move your aimer all over the place when you can just keep it in a smaller area and waste less time moving from target to target. Keep trying too, at first I thought this would be impossible but each time I did it I got a little closer to the reward and after about 15-20 minutes I had the Red Dragon.
I doubt many people will trade for this because it's so hard to get, I think people would only be willing to trade for the Axe obtained from the Crucible, as every other legendary isn't too hard too obtain.
That's all the advice I can give, it does seem impossible but you will get it eventually. You'll notice that with each round you get a little better. Stick with it.