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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
7mm Ultramag, Freebore & Accuracy
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<blockquote data-quote="J E Custom" data-source="post: 646763" data-attributes="member: 2736"><p>Freebore has long been a controversial subject.</p><p></p><p>There are two definite schools of though, One is to get accuracy you must seat against the lands.</p><p>(Benchresters often do this for round to round consistency) but they are not using cartriges that</p><p>will hold 100+ grains of powder.</p><p></p><p>The other faction is the "Freebore dont scare me" group. these are the shooters that shoot the </p><p>over bore cartriges in order to achieve Warp Speed from there bullets without the problems of</p><p>excessive pressure.</p><p></p><p>One poster said that his gunsmith said it was a mater of presenting the bullet to the lands</p><p>squarely.This is very true.</p><p></p><p>Freebore is a distance that the bore (Same diameter as the bullet) of the barrel has no rifling.</p><p>This allows the bullet to start moving before it engages the rifling lowering the initial pressure</p><p>required to engrave the bullet. This allows the use of more powder,producing more gas,to </p><p>propel the bullet faster in a longer barrel where it can be used.</p><p></p><p>Contradictory to some peoples belief, Roy Weatherby Did know what he was doing and proved </p><p>it by loading the fastest cartriges in the world for a time. As to the amount of required Freebore</p><p>the cartrige designer determines that based on what he is looking for (The reason for coming</p><p>up with a new cartrige to fill a gap left by others). Most of the Weatherbys have a generous</p><p>amount of Freebore 0.361 to 0.756. In spite of this they can be very accurate if chambered </p><p>and loaded well still using the standard Freebore (SAMMI).</p><p></p><p>The big 7mm RUM is extreemly overboard and needs plenty of freebore and longer barrels to </p><p>reach it's potential. Top velocity and trajectory can be reached with bullets in the 140 to 160 grain</p><p>class with the 168 match bullets not far behind. It is my opinion that is is a great choice if</p><p>someone want's to use the 175 to 200 grain 7mm bullets for high wind areas and shooting.</p><p>But if flat shooting is what you want the 140s 150s and 160 are the way to go.</p><p></p><p>All of my big Magnums have SAMMI Freebore and will shoot under 1/4 moa with some shooting</p><p>less than 1/10 MOA Some are belted and some are not (Another controversy for another day).</p><p>and they are all loaded to magizne length for quick follow up shots if needed.</p><p></p><p>The trick to accuracy with lots of Freebore is simple. Concentric chambers that fit the brass perfict</p><p>with little or no head space (Less than .0005 to .0001) and concentric ammo with little or no runout.</p><p>The rest of it is good load componants for the bullet weight.</p><p></p><p>Some will not agree with this philosophy and that's not a problem but it works for me and I </p><p>believe in it because it works.</p><p></p><p>So chamber the big 7mm RUM with a SAMMI chamber and Freebore, Load good ammo and enjoy</p><p>one of the flattest shooting cartriges in the world and if you use premium bullets that perform well </p><p>on game it will be a joy to own and shoot,</p><p></p><p>J E CUSTOM</p></blockquote><p></p>
[QUOTE="J E Custom, post: 646763, member: 2736"] Freebore has long been a controversial subject. There are two definite schools of though, One is to get accuracy you must seat against the lands. (Benchresters often do this for round to round consistency) but they are not using cartriges that will hold 100+ grains of powder. The other faction is the "Freebore dont scare me" group. these are the shooters that shoot the over bore cartriges in order to achieve Warp Speed from there bullets without the problems of excessive pressure. One poster said that his gunsmith said it was a mater of presenting the bullet to the lands squarely.This is very true. Freebore is a distance that the bore (Same diameter as the bullet) of the barrel has no rifling. This allows the bullet to start moving before it engages the rifling lowering the initial pressure required to engrave the bullet. This allows the use of more powder,producing more gas,to propel the bullet faster in a longer barrel where it can be used. Contradictory to some peoples belief, Roy Weatherby Did know what he was doing and proved it by loading the fastest cartriges in the world for a time. As to the amount of required Freebore the cartrige designer determines that based on what he is looking for (The reason for coming up with a new cartrige to fill a gap left by others). Most of the Weatherbys have a generous amount of Freebore 0.361 to 0.756. In spite of this they can be very accurate if chambered and loaded well still using the standard Freebore (SAMMI). The big 7mm RUM is extreemly overboard and needs plenty of freebore and longer barrels to reach it's potential. Top velocity and trajectory can be reached with bullets in the 140 to 160 grain class with the 168 match bullets not far behind. It is my opinion that is is a great choice if someone want's to use the 175 to 200 grain 7mm bullets for high wind areas and shooting. But if flat shooting is what you want the 140s 150s and 160 are the way to go. All of my big Magnums have SAMMI Freebore and will shoot under 1/4 moa with some shooting less than 1/10 MOA Some are belted and some are not (Another controversy for another day). and they are all loaded to magizne length for quick follow up shots if needed. The trick to accuracy with lots of Freebore is simple. Concentric chambers that fit the brass perfict with little or no head space (Less than .0005 to .0001) and concentric ammo with little or no runout. The rest of it is good load componants for the bullet weight. Some will not agree with this philosophy and that's not a problem but it works for me and I believe in it because it works. So chamber the big 7mm RUM with a SAMMI chamber and Freebore, Load good ammo and enjoy one of the flattest shooting cartriges in the world and if you use premium bullets that perform well on game it will be a joy to own and shoot, J E CUSTOM [/QUOTE]
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