I have 3 calibers in question one is a 300 RUM 26 in barrel I am planing on useing retumbo and the 208 amax but what primer the next is a 270 winchester i hace not got powder for this was hoping for this gun to have good accuracy out to 650 700 yd. but am not sure on what powder bullets and primer combo 22 in barrel I was planning on IMR 4198 with a 40 gr. vmax but not sure on primer for the 204 its a 26 in heavy barrel. any help would be great. thanks jim