Nope won't work, listen to Ben, he's been there done that. I recommend a minimum of 900 grains for buff arrows and that is with the arrow flying perfectly and the right head. Imo 70#'s is right at the mimimum for buff, so you need to have your arrow perfect. The only GT that you have a chance with is the Big Game 100+, I shoot them out of my 73# Black Widow, cut to 30.5" AND I still have to use the weight system to get enough spine and even at that they only come out to a little over 700 grains. I'm not really fond of using the rear weights on super tough animals like water buff, since I think they increase flex in the shaft upon impact and impede penetration. Weight tubes will add weight, but they also reduce spine. You can go with the heavy Grizzlystiks, but they will be a bit low on the weight side. You didn't say what your draw length is, but if is shorter than mine, you may be able to get by with a weighted GT 100, otherwise your options are a heavy wood shaft or a duplex, shaft inside a shaft.