It is based on a Sako magnum action. Earlier this week, I decided to load up a bunch of .257 Weatherby Magnum ammo and work on finding the secret sauce for an accurate load. 257 WEATHERBY MAGNUM. We used the Winchester large rifle magnum primer in Weatherby brass throughout our tests. As we can see, the 257 Weatherby Magnum shoots much flatter than the Creedmoor. 257 Wby Magnum 110 gr ELD-X ® Precision Hunter ® Item #81364 | 20/Box . For this reason, it is generally not possible to seat a bullet close to, or in contact with the lands (rifling). The Creedmoor load will launch at 2,730 fps from a 24” barrel, the 257 Weatherby Magnum at 3433 fps from a 26” tube. I resized all my brass (both the Weatherby and the Hornady brass), tumbled it until the stuff glistened, and then tried to chamber it. Ballistic Table . Not sure if that bullet could handle the strain, might come apart. It also has Weaver 4-16X scope mounted in an EAW rings and bases. The older Weatherby rifles also had 3/4-inch of freebore, but the throating of all Weatherby rifles was changed in 1967 - 1968 to about 3/8-inch. This afternoon I loaded another 10 rounds of what is my current standard hunting load in my 257 Weatherby Magnum. 257 Weatherby: 28" #5 fluted SS Lilja 3 groove barrel, moly coated 110 accubond, .015" off rifling. I've never used military surplus powder; I probably ought to try it sometime. IMR 7828 should be a good powder to try though my load of choice is with RL-25. I don't think using necked down 270 Weatherby cases will be a problem. Once I have the rifle in my hands, and determine the twist rate, Ill get a better idea of what should work. Had to stop using 115 VLDs because rough throat combined with 3 groove began to damage VLDs causing poor groups with occasional flyers. As with most Weatherby Magnum’s, there are a few points to keep in mind when loading this cartridge. The rifle has a heavy barrel of 25 inches. The chambers have “freebore”, meaning they have a longer throat. In a case the size of the 257 Weatherby, you won't find any pressure difference when using magnum vs regular primers. Whenever I do a three-shot test group at the range this load shoots sub-MOA, typically in the 0.6 to 0.9 MOA size. That is a 110 grain Nosler Accubond with a muzzle velocity of a bit more than 3,300 fps. Son of a gun, the Hornady brass still wouldn’t allow the action to close. As for making loads either learn or pay dearly for a custom load that gets close to 4000 fps.. IMO you are better off buying ammo with 100-120 gr bullets for your 257 Weatherby if you don't reload. Accuracy and terminal performance are the cornerstones of Hornady ® Precision Hunter ® factory loaded ammunition. Fired at sea level, 10 mph right angle wind. Most belted mags headspace on the shoulder - not the belt. The .257 Weatherby Magnum dates back to 1943, when Roy Weatherby began experimenting with the .300/.375 H&H Magnum case for a series of wildcat cartridges, most of which later became proprietary and today are SAAMI standardized. Great care has been given by Hornady engineers to develop superior, match­-accurate hunting loads that allow the ELD­-X ® bullet to achieve its maximum ballistic potential. Gunpowder Charge Weight Velocity m/s Velocity fps; Norma MRP: Max 75.1 Min 71.0: 1146 1018: 3760 3340 I do see IMR 4831 as an accuracy powder in the 257 Weatherby Mag load for data, for certain weights -mostly the lighter bullets. Alliant Reloder 26 Weatherby CCI 250 59.3 2901 65.9 Vihtavuori N560 Federal CCI 250 60.0 2963 64.0 Alliant Reloder 23 Weatherby CCI 250 60.8 3031 64.2 Hodgdon Retumbo Federal CCI 250 65.0 2948 69.0 Alliant Power Pro 4000-MR Weatherby CCI 250 56.9 2920 61.9 IMR 7977 Weatherby CCI 250 62.1 2875 68.9 Alliant Reloder 22 Federal CCI 250 59.0 2904 63.0 We’re sticking with published data. The following data was developed in a custom rifle built by August Francotte of Belgium. Originally, Weatherby .257 Magnum rifles had a 1:12” twist, but the rate was later increased to 1:10” to handle longer, heavier bullets. Shoulder - not the belt gr ELD-X ® Precision Hunter ® factory loaded ammunition to try sometime...: 28 '' # 5 fluted SS Lilja 3 groove barrel, moly coated accubond... My hands, and determine the twist rate, Ill get a better of. 3,300 fps try it sometime in Weatherby brass throughout our tests,.015 '' off rifling loaded ammunition throughout tests... 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