I was in the same situation awhile back. Trying to decide between the guide gun in 45/70 or .450. I plan on getting the 45/70 just because of the availablity of ammo. I dont reload so i have to stick to what is on the shelf. So far i have seen only one manufacture making loads for the the .450, while there are plenty for the 45/70. When i finally do buy my guide gun it will be in the old 45/70