Ras308: Iowegun is 100 percent correct. The chances are good that you do have a fast-twist barrel, which will stabilize the heavier bullets, although they can shoot the 139 grain bullets like it was said by slowing down the velocity of the lighter bullets. I own a CZ 550 in 7x57mm. It has a 1x8.66 twist. Ruger Mark IIs have twists of 1x9.5 and the Winchester Model 70 Featherweight in 7x57mm has a twist of 1x10. With my rifle, I shoot Hornady 162 grain SSTs and the 160 grain Nosler Partition and H414 powder. I also used H414 powder in the Ruger with good success. I chronographed my loads and with the 162 grain SST, loaded way, way out so the bullet was but .01 inch from the lands (3.30 OAL) I am getting 2,815 fps. Keep in mind my rifle has a 23.6 inch barrel. With the SST I can get .480 inch three-shot groups from a sandbag rest at 100 yards. One time I shot a .216 inch center-to-center group. With the partitions also loaded .01 inch from the lands, with the same powder charge, the load chronographs at 2,835 fps average and prints into groups just below three quarters of an inch, like .70 and sometimes less. My brother liked my rifle so much he bought a CZ 550 Full Stock in 7x57mm, with a 20.5 inch barrel and the same barrel twist as my rifle, 1x8.66 inches. His rifle hates the SST bullets, but loves the 160 grain Partition seated just off the lands. We chronographed his rifle with the partition and were getting a bit more than 2,700 fps in nice little .75 inch groups. To be honest, I have just never considered the 139 grain bullet in my rifle and my brother is more than happy with his rifle and load. I have used my 7x57mm on elk, mule deer, whitetail deer, antelope, wild hogs, javelina, coyote and even a wild turkey in Texas. I have a buddy who shoots the Model 70 Featherweight in 7x57mm and it likes the 150 grain Partition with H4350 powder. Guess what I am saying is give the 139 grain bullets a try, but don't give up if they do not shoot as well as you would like them to shoot. Pick up some 160 grain bullets or the 162 grain Hornady, find out with those bullets the overall length of the cartridge, push it back .01 to .025 of an inch from the lands, put some of the H414 powder in the case and see what happens. Have fun with that rifle if you get it. The 7x57mm is one of the most underrated calibers there is. I have even taken elk with it out to 325 yards or so. Hit right in the boiler room the elk hunched up a bit, sat back and then fell over and was dead. It is a wonderful caliber. Tom Purdom
