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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
5 R canted land barrels.
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<blockquote data-quote="Bart B" data-source="post: 110374" data-attributes="member: 5302"><p>Barret (Boots) Obermeyer came up with his 5R rifling design soon after Sierra Bullets introduced their 7mm 168-gr. HPMK bullet my very good friend Tom Treinen used with a borrowed rifle and ammo in 1970 to break the 1000-yard scope sight match record at the highpower Nationals; 42 shots inside 20 inches, prone, windy conditions. Problem with those bullets was their jackets were a bit thin in order for Sierra to get uniform wall thickness for a very long jacket in that caliber. Those thin jackets were engraved a bit too much by conventional rifling and they would occasionally split at a engraved land mark and fly apart. Boots Obermeyer designed the 5R rifling so that less stress was made at the edges of the engraved groove in the bullets. That worked well enough indeed. But Sierra had problems making that bullet as accurate as their 30 caliber ones as jackets just couldn't be made to wall thickness uniformity quite as good as the 30 caliber ones. Those bullets Tom Treinen used were taken out of the final pointing machine as they were tested and found to be very accurate in firing tests.</p><p></p><p>Meanwhile, Boots Obermeyer made some 30 caliber match barrels with 5R rifing. These shot as good and often better than his conventional rifling. His 5R became quite popular afterwords.</p><p></p><p>Mike Rock was an apprentice under Boots Obermeyer and there's rumors/facts going around that Mike left Boots' shop under less than aimiable (hostile?) conditions. And Mike Rock took a lot of skills and knowledge with him. Including the 5R rifling design.</p><p></p><p>I've used both conventional and 5R barrels from Obermeyer; both with the same bore and groove diameters. With the same load for .30-.338 Win. Mag. cartridges, muzzle velocity was within 10 fps of each other. Accuracy was too close between them to say one was better than the other; 15-shot groups at 1000 yards in the 5 to 6 inch range.</p></blockquote><p></p>
[QUOTE="Bart B, post: 110374, member: 5302"] Barret (Boots) Obermeyer came up with his 5R rifling design soon after Sierra Bullets introduced their 7mm 168-gr. HPMK bullet my very good friend Tom Treinen used with a borrowed rifle and ammo in 1970 to break the 1000-yard scope sight match record at the highpower Nationals; 42 shots inside 20 inches, prone, windy conditions. Problem with those bullets was their jackets were a bit thin in order for Sierra to get uniform wall thickness for a very long jacket in that caliber. Those thin jackets were engraved a bit too much by conventional rifling and they would occasionally split at a engraved land mark and fly apart. Boots Obermeyer designed the 5R rifling so that less stress was made at the edges of the engraved groove in the bullets. That worked well enough indeed. But Sierra had problems making that bullet as accurate as their 30 caliber ones as jackets just couldn't be made to wall thickness uniformity quite as good as the 30 caliber ones. Those bullets Tom Treinen used were taken out of the final pointing machine as they were tested and found to be very accurate in firing tests. Meanwhile, Boots Obermeyer made some 30 caliber match barrels with 5R rifing. These shot as good and often better than his conventional rifling. His 5R became quite popular afterwords. Mike Rock was an apprentice under Boots Obermeyer and there's rumors/facts going around that Mike left Boots' shop under less than aimiable (hostile?) conditions. And Mike Rock took a lot of skills and knowledge with him. Including the 5R rifling design. I've used both conventional and 5R barrels from Obermeyer; both with the same bore and groove diameters. With the same load for .30-.338 Win. Mag. cartridges, muzzle velocity was within 10 fps of each other. Accuracy was too close between them to say one was better than the other; 15-shot groups at 1000 yards in the 5 to 6 inch range. [/QUOTE]
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5 R canted land barrels.
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