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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
7MM - Need to make a choice
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<blockquote data-quote="MontanaRifleman" data-source="post: 837381" data-attributes="member: 11717"><p>Back on track...</p><p></p><p>Let's do a little mathematical comparison using the 7 STW. 300 RUM and 308 Win</p><p></p><p>Both the 300 RUM and 308 Win have the same bore cross section area of .074 sq inches. They have 107.2 and 55.8 gr of water capacity each, respectively.</p><p></p><p>The 7 STW has a bore cross section of .063 square inches and 92.7 gr of water capacity.</p><p></p><p>If we divide the capacity by the area of these cartridges for a relative "overbore" comparison we get the following...</p><p></p><p>308 Win, 749</p><p>300 RUM, 1440</p><p>7 STW, 1464</p><p></p><p>The higher the number, the more "overbore" the cartridge.</p><p></p><p>If you were to ask the question, "how much barrel life could one expect from the 300 RUM" in this forum, the most common answer will probably be about 1000 of good accuracy if you take good care of it. That question has been asked a number of times and to the best of my memory, 1000 was the most common answer.</p><p></p><p>Now there are some other factors to consider as far as throat wear is concerned. Assuming shooting the same pressures, rate of fire, etc., the the angle of the shoulder and length of neck will have an effect on throat wear. The sharper the shoulder and longer the neck in proportion to its diameter, the slower the rate of throat erosion.</p><p></p><p>The RUM has about the same length of neck proportionally as the STW, however the RUM has a sharper shoulder of 30* vs 25* for the STW. A slight difference.</p><p></p><p>If we accept that 1000 rounds of barrel life out of the RUM, then it would be reasonable to expect a slightly less number of rounds out of the STW based on overbore factor and shoulder design. This is also consistent with what I experienced with my 7 RM.</p><p></p><p>There are no hard and fast rules... every barrel is different and there are always exceptions to the rule - like my 25-06 which shot amazingly well after the tube was long since fried. Had to clean the **** out of it now and then, but it shot very well.</p><p></p><p>The bottom line is the magnums are overbore throat eaters and the more powder, fire and pressure you force through the throat, the faster it is going to burn. That is the price of speed. Always has been and always will be. No free lunch.</p></blockquote><p></p>
[QUOTE="MontanaRifleman, post: 837381, member: 11717"] Back on track... Let's do a little mathematical comparison using the 7 STW. 300 RUM and 308 Win Both the 300 RUM and 308 Win have the same bore cross section area of .074 sq inches. They have 107.2 and 55.8 gr of water capacity each, respectively. The 7 STW has a bore cross section of .063 square inches and 92.7 gr of water capacity. If we divide the capacity by the area of these cartridges for a relative "overbore" comparison we get the following... 308 Win, 749 300 RUM, 1440 7 STW, 1464 The higher the number, the more "overbore" the cartridge. If you were to ask the question, "how much barrel life could one expect from the 300 RUM" in this forum, the most common answer will probably be about 1000 of good accuracy if you take good care of it. That question has been asked a number of times and to the best of my memory, 1000 was the most common answer. Now there are some other factors to consider as far as throat wear is concerned. Assuming shooting the same pressures, rate of fire, etc., the the angle of the shoulder and length of neck will have an effect on throat wear. The sharper the shoulder and longer the neck in proportion to its diameter, the slower the rate of throat erosion. The RUM has about the same length of neck proportionally as the STW, however the RUM has a sharper shoulder of 30* vs 25* for the STW. A slight difference. If we accept that 1000 rounds of barrel life out of the RUM, then it would be reasonable to expect a slightly less number of rounds out of the STW based on overbore factor and shoulder design. This is also consistent with what I experienced with my 7 RM. There are no hard and fast rules... every barrel is different and there are always exceptions to the rule - like my 25-06 which shot amazingly well after the tube was long since fried. Had to clean the **** out of it now and then, but it shot very well. The bottom line is the magnums are overbore throat eaters and the more powder, fire and pressure you force through the throat, the faster it is going to burn. That is the price of speed. Always has been and always will be. No free lunch. [/QUOTE]
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