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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Independent Study: LRH calibres - 7mm WSM vs 300 RUM vs 338 LM
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<blockquote data-quote="Bart B" data-source="post: 632919" data-attributes="member: 5302"><p><strong>Re: 338 Norma Mag? How much is too much?</strong></p><p></p><p>Regarding my barrel life numbers.....Since the 1960's, I've observed that the most accurate cartridges burn about 1 grain of powder for each square millimeter of the bore's cross sectional area. By that, I mean sub 1/4 MOA at 100 yards, 1/3 at 300, 1/2 at 600 and 3/4 MOA at 1000 yards. Examples are the .222 Rem. and 22 or 6mm PPC benchrest cartridges popular in short range group shooting. Others are the .308 Win. which was popular for 35 years for high power competition. Most notable with these cartridges is they all deliver that accuracy level for about 3000 rounds. So I established a definition of "bore capacity" as one grain of powder for each square millimeter of bore cross sectional area.</p><p></p><p>Increasing the powder charge by 40% for any successful caliber used in competition tends to cut accurate barrel life by 50%; it drops to 1500 rounds. Doubling the charge weight for a given caliber over its bore capacity ends up with 1/4 the barrel life; 750 rounds. When 30 caliber magnums were popular for long range prone matches, they got about 1200 rounds of accurate barrel life. After my friend set the 1000 yard record at the 1970 Nationals with a borrowed 7mm Rem Mag, it became popular for that course of fire but it got only about 800 rounds of accurate barrel life. My own .264 Win. Mag barrel died at 640 rounds.</p><p></p><p>Learning what top competitive shooters get for barrel life in all sorts of cartridges showed me my formula is pretty darned accurate. It's been so for all the barrels I wore out shooting matches and testing them for accuracy in. Sierra Bullets' data on barrel life in their test barrels agrees almost exactly with my calculations.</p><p></p><p>The above aside, rifle barrels whose accuracy is less will have a longer barrel life. One starting out with 1/2 MOA accuracy at 100 yards will have double the life. If the barrel's a 3/4 to 1 MOA tube, it will get 4 times the life. Standard service rifle barrels in 5.56mm and 30 caliber go about 10 to 12 thousand rounds before they need replacing. All this is why most folks claim (and therefore get) longer barrel life. Their barrels plus their abilities don't start out with the accuracy levels I'm referencing so naturally they get longer barrel life because they're using a different standard. Best example is a .22 rimfire barrel life; most folks think they'll last for hundreds of thousands of rounds but those kids on the Olympic teams get only 30,000 or so rounds per barrel before it needs replacing to meet their requirements.</p><p></p><p>So, with the .338 Lapua Mag, if it starts out shooting no worse than 3/4 MOA at 1000 yards, I think it'll hold that level of accuracy for about 1200 rounds. It's bore capacity is about 59 grains and it uses about 95 grains of powder per charge. If its accuracy is about 1 MOA at 1000 yards, its barrel will go about 1500 rounds according to my calculations.</p></blockquote><p></p>
[QUOTE="Bart B, post: 632919, member: 5302"] [b]Re: 338 Norma Mag? How much is too much?[/b] Regarding my barrel life numbers.....Since the 1960's, I've observed that the most accurate cartridges burn about 1 grain of powder for each square millimeter of the bore's cross sectional area. By that, I mean sub 1/4 MOA at 100 yards, 1/3 at 300, 1/2 at 600 and 3/4 MOA at 1000 yards. Examples are the .222 Rem. and 22 or 6mm PPC benchrest cartridges popular in short range group shooting. Others are the .308 Win. which was popular for 35 years for high power competition. Most notable with these cartridges is they all deliver that accuracy level for about 3000 rounds. So I established a definition of "bore capacity" as one grain of powder for each square millimeter of bore cross sectional area. Increasing the powder charge by 40% for any successful caliber used in competition tends to cut accurate barrel life by 50%; it drops to 1500 rounds. Doubling the charge weight for a given caliber over its bore capacity ends up with 1/4 the barrel life; 750 rounds. When 30 caliber magnums were popular for long range prone matches, they got about 1200 rounds of accurate barrel life. After my friend set the 1000 yard record at the 1970 Nationals with a borrowed 7mm Rem Mag, it became popular for that course of fire but it got only about 800 rounds of accurate barrel life. My own .264 Win. Mag barrel died at 640 rounds. Learning what top competitive shooters get for barrel life in all sorts of cartridges showed me my formula is pretty darned accurate. It's been so for all the barrels I wore out shooting matches and testing them for accuracy in. Sierra Bullets' data on barrel life in their test barrels agrees almost exactly with my calculations. The above aside, rifle barrels whose accuracy is less will have a longer barrel life. One starting out with 1/2 MOA accuracy at 100 yards will have double the life. If the barrel's a 3/4 to 1 MOA tube, it will get 4 times the life. Standard service rifle barrels in 5.56mm and 30 caliber go about 10 to 12 thousand rounds before they need replacing. All this is why most folks claim (and therefore get) longer barrel life. Their barrels plus their abilities don't start out with the accuracy levels I'm referencing so naturally they get longer barrel life because they're using a different standard. Best example is a .22 rimfire barrel life; most folks think they'll last for hundreds of thousands of rounds but those kids on the Olympic teams get only 30,000 or so rounds per barrel before it needs replacing to meet their requirements. So, with the .338 Lapua Mag, if it starts out shooting no worse than 3/4 MOA at 1000 yards, I think it'll hold that level of accuracy for about 1200 rounds. It's bore capacity is about 59 grains and it uses about 95 grains of powder per charge. If its accuracy is about 1 MOA at 1000 yards, its barrel will go about 1500 rounds according to my calculations. [/QUOTE]
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Independent Study: LRH calibres - 7mm WSM vs 300 RUM vs 338 LM
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