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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Balance in bore diameter???
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<blockquote data-quote="Bart B" data-source="post: 104682" data-attributes="member: 5302"><p>Fiftydriver's comments are pretty good and explain things well. Here's some observations I've made over the years.</p><p></p><p>For each caliber, there seems to be a few cartridges that seem to attain the best accuracy. These cartridges are the ones often used in competition and tend to produce the best scores. They all have one thing in common; their powder charge weight is at or very near 'bore capacity.'</p><p></p><p>OK, so what is bore capacity? Years ago a 'smith catering to the benchrest crowd explained it to me as follows. Bore capacity in grains of powder is equal to the cross sectional area of the bore in square millimeters; 1 grain of powder for each square millimeter. I did some checking and here's what I learned comparing the bore capacity for different calibers and examples of very accurate cartridges for them:</p><p></p><p>22 caliber, bore capacity = 26 grains; .22 PPC, .222 Rem.</p><p>24 caliber, bore capacity = 28 grains, 6mmPPC, 6mmBR</p><p>26 caliber, bore capacity = 33 grains, .260 Rem.</p><p>27 caliber, bore capacity = 38 grains, 7mm-08</p><p>30 caliber, bore capacity = 45 grains, .308 Win.</p><p></p><p>That 'smith also said that when cartridges at bore capacity are used, barrels typically last about 3000 to 4000 rounds of best accuracy. Double the powder charge over bore capacity for a given bore and barrel life drops to 1/4th as many; 750 to 1000 rounds.</p><p></p><p>Interesting stuff but it seems to be correct. There's a bunch of meanings/definitions for bore capacity, but this one makes the most sense to me.</p></blockquote><p></p>
[QUOTE="Bart B, post: 104682, member: 5302"] Fiftydriver's comments are pretty good and explain things well. Here's some observations I've made over the years. For each caliber, there seems to be a few cartridges that seem to attain the best accuracy. These cartridges are the ones often used in competition and tend to produce the best scores. They all have one thing in common; their powder charge weight is at or very near 'bore capacity.' OK, so what is bore capacity? Years ago a 'smith catering to the benchrest crowd explained it to me as follows. Bore capacity in grains of powder is equal to the cross sectional area of the bore in square millimeters; 1 grain of powder for each square millimeter. I did some checking and here's what I learned comparing the bore capacity for different calibers and examples of very accurate cartridges for them: 22 caliber, bore capacity = 26 grains; .22 PPC, .222 Rem. 24 caliber, bore capacity = 28 grains, 6mmPPC, 6mmBR 26 caliber, bore capacity = 33 grains, .260 Rem. 27 caliber, bore capacity = 38 grains, 7mm-08 30 caliber, bore capacity = 45 grains, .308 Win. That 'smith also said that when cartridges at bore capacity are used, barrels typically last about 3000 to 4000 rounds of best accuracy. Double the powder charge over bore capacity for a given bore and barrel life drops to 1/4th as many; 750 to 1000 rounds. Interesting stuff but it seems to be correct. There's a bunch of meanings/definitions for bore capacity, but this one makes the most sense to me. [/QUOTE]
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Balance in bore diameter???
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