Whitetails & muskies, I have used arrows like ELKINMTCWB for the last 7 years with good results. With that said my friend came with me for 2 years and came back with two bulls. A four point bull and a six point bull, both of those bulls were big bodied and were killed with 400 grain Gold Tips. Out of the two bulls one was a pass through and the other was not, but the penetration was excellent. He was using Muzzy's and shooting his Mathews Q2XL at 65#. Like I have stated before I have used XX75's 2219 580 grain arrows to kill elk. Before that I used 2413 that weighed 500 grains to kill elk with good results too. I have had one bull elk that I didn't have a pass through either. I pulled the shot high and foward and ended up hiting the shoulder bone. I hit the lungs, barely, it was high and through the top of them. In case you are wondering the shot was only 15 yards away and broadside. I was a little too excited and pulled the shot, I admit I was lucky and thankful to not lose that bull. With making the switch to Gold Tips this year I am playing around with the add on weights and weighted straws to make my arrow heavier. I don't want to hunt with an arrow below 450 grains and do pefer it around 480 to 500 grains. Thats my personal choice, not saying a 400 grain arrow will not get the job done because it sure will. With a CUC broadhead like the Steelforce you should have no problems at all with a carbon arrow even if its only 400 grains. My wife will use a 400 grain arrow with a CUC this year, because her bow is 42# (thats the max she can pull and shoot accuratel) she will have to limit her shots to 25 yards max. Hopefully she kills a elk, the hard part will be finding a babysittter to watch our kids for a saturday or two. Getting the elk under 25 yards well that will be up to me.