I have two 6.5 Rem Mags one in a 20" 660 and the other in a flatbolt 22" Ruger 77. Great caliber. My 660 has a one shot string on caribou that I have lost count over. The gun writers of the time didn't understand the concept of short magnum and killed it with bad press that was mostly silly. Run the consequences of deep seating skinny little 6.5 bullets into a ballistics calculator and you lose maybe 25 ft/sec. The short barrels do give up some steam as in a long barrel this caliber comes close to matching the 264 Win Mag. However in 20" guise it's as handy as can be and matches 270 ballistics. The 22" gets 70-90 extra feet/sec and is an entirely useful package.
