Yes it will fit into a short action as that is what I have. On regards as to if the 243 win chamber is concerned I beleive that RR has a valid point. Your smith will enlighten you on this.

You are going to have to form 6mmx284 brass. With the 6.5x284 brassbeing available now it's simply a matter of running it through a 6mmx284 FL/neck sizing die. I have always used 284 Win brass with a form die that necks it to 25 cal and then run through the 6mm sizer. Either way, it's no big deal. For sure the 6.5 brass is the way togo these days. Norma and Hornady make it.

As far as I know the 55 gr Nosler Ballistic Tip is the lightest, they are great for impressive speed but dont have the B.C. for the longer ranges.