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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Big Seven Case Capacities
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<blockquote data-quote="Austin" data-source="post: 29890" data-attributes="member: 1956"><p>After coming upon this forum, I found that you are trying do exactly what I have been working on for some time now. I currently have a rifle chambered for a .338 Lap necked down to 7mm. It is based on a Remington action, has a 28" Pac-Nor 1:9" SuperMatch bbl, blueprinted/trued action and bolt face, heavy recoil lug, Sako extractor, bbl is free floated and is glass/pillar bedded into a blue-laminate, tactical-style stock. It has an adjustable butt-plate with a kick-eeze pad installed. It is a hard-core powder burner. The cartridge is called a Big 7 TurnerBurner. It is one of the proprietary cartridges from a local gunsmith here. We decided we would try something new and build the rifle with a 1:9" bbl and take advantage of the 130, 140, and 154gr. bullets (which are perfect for Texas whitetail!). It loves the 140gr Ballistic Silver-Tips from Nosler and it burns about 109.5grs. WC872 with the bullet seat right at the lands. On lighter loads of about 100.0grs and the same bullet, chrono readings were 3685, 3649, and 3693 for three shots. With the heavier bullets, such as the 168gr. Sierra MatchKings, pressure signs become evident at 107.5grs. of H870. This appears to be the limit for this bullet / powder combo and would say the max safe load would be about 102.5 - 105.0 grs. I am currently working on developing more load data for the 162gr A-Max which is running pretty close to the same capactity as the 168 grainers. So far, H870 has had some problems with hang-fires at loads below 100grs. (tried two different primers, so detonation is more suspect since this cartridge seems to prefer charges &gt; 88% with H870) Between 102.5 and 105grs. H870 looks like a good comfortable area for my rifle with a 168gr. Sierra MK and a Fed 215 primer. WC872 has shown VERY promising results without hang-fires also. Will report more on this later. </p><p> The cases are Norma .338 Lapua Mag and were made by necking them down in a two step process, fire-forming with a 140gr bullet seated on the lands on top of 17grs. Unique. After initial fire-forming, cases are annealed, and shot with a full load to complete the fire-form process. After this, cases are all trimmed to a length of 2.715", flash holes deburred, primer pocket reamed, and then, culled by weight. Final case capacity is 116.3grs H2O. </p><p> I am doing some final work on the stock, so I will be running some 130gr. MatchKings on top of 112grs. WC872 through the chrono some time next week when I finish. I will publish more ballistic/load data as I gather it. I'll let you know my results soon. Maybe some pics also. </p><p></p><p>One more note: When building this caliber, I have noticed that throat size becomes critical. Many times, with the 130gr. bullets, I am seating only .191" of the bullet in order to make contact with the lands. Usually, I seat right on the lands and drop my powder charges back, but I have had to seat at .005" - 009" off the lands with the 140gr bullets to maintain sufficient bullet pull. With this twist, the throat could stand to be .008 - .010" shorter for the lighter bullets. Have not really shot for accuracy too much yet, but 140gr. Nosler BT's were hitting at under 1/2" mark at 100yds. Seems to be an EXTREMELY flat, accurate shooter so far, just needs more time in development.</p><p></p><p>So far, COAL for tested bullets is as follows:</p><p></p><p>All bullets seated to contact with lands.</p><p></p><p>162gr. Hornady A-Max: 3.818"</p><p>168gr. Sierra MatchKing: 3.705"</p><p>140gr. Nosler Bal. Tip.: 3.702"</p><p></p><p>[ 01-07-2004: Message edited by: Austin ]</p></blockquote><p></p>
[QUOTE="Austin, post: 29890, member: 1956"] After coming upon this forum, I found that you are trying do exactly what I have been working on for some time now. I currently have a rifle chambered for a .338 Lap necked down to 7mm. It is based on a Remington action, has a 28" Pac-Nor 1:9" SuperMatch bbl, blueprinted/trued action and bolt face, heavy recoil lug, Sako extractor, bbl is free floated and is glass/pillar bedded into a blue-laminate, tactical-style stock. It has an adjustable butt-plate with a kick-eeze pad installed. It is a hard-core powder burner. The cartridge is called a Big 7 TurnerBurner. It is one of the proprietary cartridges from a local gunsmith here. We decided we would try something new and build the rifle with a 1:9" bbl and take advantage of the 130, 140, and 154gr. bullets (which are perfect for Texas whitetail!). It loves the 140gr Ballistic Silver-Tips from Nosler and it burns about 109.5grs. WC872 with the bullet seat right at the lands. On lighter loads of about 100.0grs and the same bullet, chrono readings were 3685, 3649, and 3693 for three shots. With the heavier bullets, such as the 168gr. Sierra MatchKings, pressure signs become evident at 107.5grs. of H870. This appears to be the limit for this bullet / powder combo and would say the max safe load would be about 102.5 - 105.0 grs. I am currently working on developing more load data for the 162gr A-Max which is running pretty close to the same capactity as the 168 grainers. So far, H870 has had some problems with hang-fires at loads below 100grs. (tried two different primers, so detonation is more suspect since this cartridge seems to prefer charges > 88% with H870) Between 102.5 and 105grs. H870 looks like a good comfortable area for my rifle with a 168gr. Sierra MK and a Fed 215 primer. WC872 has shown VERY promising results without hang-fires also. Will report more on this later. The cases are Norma .338 Lapua Mag and were made by necking them down in a two step process, fire-forming with a 140gr bullet seated on the lands on top of 17grs. Unique. After initial fire-forming, cases are annealed, and shot with a full load to complete the fire-form process. After this, cases are all trimmed to a length of 2.715", flash holes deburred, primer pocket reamed, and then, culled by weight. Final case capacity is 116.3grs H2O. I am doing some final work on the stock, so I will be running some 130gr. MatchKings on top of 112grs. WC872 through the chrono some time next week when I finish. I will publish more ballistic/load data as I gather it. I'll let you know my results soon. Maybe some pics also. One more note: When building this caliber, I have noticed that throat size becomes critical. Many times, with the 130gr. bullets, I am seating only .191" of the bullet in order to make contact with the lands. Usually, I seat right on the lands and drop my powder charges back, but I have had to seat at .005" - 009" off the lands with the 140gr bullets to maintain sufficient bullet pull. With this twist, the throat could stand to be .008 - .010" shorter for the lighter bullets. Have not really shot for accuracy too much yet, but 140gr. Nosler BT's were hitting at under 1/2" mark at 100yds. Seems to be an EXTREMELY flat, accurate shooter so far, just needs more time in development. So far, COAL for tested bullets is as follows: All bullets seated to contact with lands. 162gr. Hornady A-Max: 3.818" 168gr. Sierra MatchKing: 3.705" 140gr. Nosler Bal. Tip.: 3.702" [ 01-07-2004: Message edited by: Austin ] [/QUOTE]
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