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Rifles, Reloading, Optics, Equipment
Reloading
300 RUM- early pressure signs?
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<blockquote data-quote="mrultramag" data-source="post: 1039549" data-attributes="member: 4467"><p>first off the data in the manuals is for factory rifles using SAMMI chamber and throat. The 300 rum is designed with a long throat (free bore). The factory magazine on a model 700 will only allow your cartridge overall length to be 3.670 or thereabouts. in a factory rifle 300 rum you cannot seat the bullet far enough out to reach the lands usually.</p><p>You are using a custom rifle and using a longer COL to place the bullet closer to the lands or your barrel was chambered with a shorter throat than SAMMI. Also your chamber may be on the tighter side since its a custom. Also your using a longer barrel. </p><p></p><p>All of this adds up to you experiencing max pressure at a lower charge powder weight than the manual indicates. Nothing surprising about that.</p><p></p><p>If the manual's testing was done with a 26" bbl. Look at the velocity they reached. Now to be safe, figure 25 additional fps for each inch of additional bbl length. So for 4 additional inches add 100 fps.</p><p>Don't worry about the fact that you are reaching this velocity with a mid level charge.</p><p>You will either hit your target velocity and be happy or you will see pressure signs which will tell you to back your load down some.</p><p></p><p>In your situation, always start your load at starting load level and progress up in charge weight carefully. A chronograph is a must for you. You have removed the "free bore" which is one of the ways the RUM cartridges and Weatherby's get their performance at acceptable pressures.</p></blockquote><p></p>
[QUOTE="mrultramag, post: 1039549, member: 4467"] first off the data in the manuals is for factory rifles using SAMMI chamber and throat. The 300 rum is designed with a long throat (free bore). The factory magazine on a model 700 will only allow your cartridge overall length to be 3.670 or thereabouts. in a factory rifle 300 rum you cannot seat the bullet far enough out to reach the lands usually. You are using a custom rifle and using a longer COL to place the bullet closer to the lands or your barrel was chambered with a shorter throat than SAMMI. Also your chamber may be on the tighter side since its a custom. Also your using a longer barrel. All of this adds up to you experiencing max pressure at a lower charge powder weight than the manual indicates. Nothing surprising about that. If the manual's testing was done with a 26" bbl. Look at the velocity they reached. Now to be safe, figure 25 additional fps for each inch of additional bbl length. So for 4 additional inches add 100 fps. Don't worry about the fact that you are reaching this velocity with a mid level charge. You will either hit your target velocity and be happy or you will see pressure signs which will tell you to back your load down some. In your situation, always start your load at starting load level and progress up in charge weight carefully. A chronograph is a must for you. You have removed the "free bore" which is one of the ways the RUM cartridges and Weatherby's get their performance at acceptable pressures. [/QUOTE]
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Reloading
300 RUM- early pressure signs?
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