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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Bore Capacity versus Barrel Life
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<blockquote data-quote="Bart B" data-source="post: 1153752" data-attributes="member: 5302"><p>In spite of TOM H's ongoing vendetta of bad mouthing most everything I post, I applaud his posting the link to different formulas including Mikecr's software. That was a good idea. Mike used my powder grains and bore area base, then improved it by adding powder heat indexes. I don't know the exact data base for cartridge barrel lifes Mike used developing his formula. I mostly used Sierra Bullets' data as their test barrels were in rail guns shot indoors at 100 yards at their California plant with 10-shot control groups opening up 50% from when the barrel was new. Sierra's tests were indoors with a very stable atmosphere and eliminated all human and rifle variables. Their data showed a gradual loss of accuracy throughout the barrel life for most cartridges. About one-fifth of my data base came from competitive shooters testing match rifles clamped in machine rests outdoors.</p><p></p><p>Comparing results between my old formula and Mike's using the same powder for a given cartridge, his gives about 20% average more round counts than mine. Partly because there are more cooler and better powders these days in the burn rates best for accuracy.</p><p></p><p>That formula in a link using bore area divided by case capacity (grains of water) to get a ratio is close to my first formula tried. I calculated the volume in cubic inches (very tedious) divided by the actual area of that hole in the barrel (SAAMI spec for minimum bore plus groove area; example, 0736 sq. in. for most 30 caliber barrels) which is about mid point between using bore diameter or groove diameter. That got too much figuring so I simplified the formula to get an approximate barrel life to show how it changes for a given caliber. </p><p></p><p>Of course, none of these formulas are exact, but they do show how barrel lives change with charge choice and weight for a given cartridge. Use your own objectives, conditions and standards then shoot your ammo until it starts missing your point of aim too far.</p></blockquote><p></p>
[QUOTE="Bart B, post: 1153752, member: 5302"] In spite of TOM H's ongoing vendetta of bad mouthing most everything I post, I applaud his posting the link to different formulas including Mikecr's software. That was a good idea. Mike used my powder grains and bore area base, then improved it by adding powder heat indexes. I don't know the exact data base for cartridge barrel lifes Mike used developing his formula. I mostly used Sierra Bullets' data as their test barrels were in rail guns shot indoors at 100 yards at their California plant with 10-shot control groups opening up 50% from when the barrel was new. Sierra's tests were indoors with a very stable atmosphere and eliminated all human and rifle variables. Their data showed a gradual loss of accuracy throughout the barrel life for most cartridges. About one-fifth of my data base came from competitive shooters testing match rifles clamped in machine rests outdoors. Comparing results between my old formula and Mike's using the same powder for a given cartridge, his gives about 20% average more round counts than mine. Partly because there are more cooler and better powders these days in the burn rates best for accuracy. That formula in a link using bore area divided by case capacity (grains of water) to get a ratio is close to my first formula tried. I calculated the volume in cubic inches (very tedious) divided by the actual area of that hole in the barrel (SAAMI spec for minimum bore plus groove area; example, 0736 sq. in. for most 30 caliber barrels) which is about mid point between using bore diameter or groove diameter. That got too much figuring so I simplified the formula to get an approximate barrel life to show how it changes for a given caliber. Of course, none of these formulas are exact, but they do show how barrel lives change with charge choice and weight for a given cartridge. Use your own objectives, conditions and standards then shoot your ammo until it starts missing your point of aim too far. [/QUOTE]
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Bore Capacity versus Barrel Life
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