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Rifles, Bullets, Barrels & Ballistics
7mm Allen Mag test rifle finished.....
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<blockquote data-quote="kac1345" data-source="post: 75182" data-attributes="member: 2172"><p>Ok Nobody string me up for this one lol! This is a Formula that seems to calculate accurate barrel life preety darn close YMMV.</p><p></p><p>C/ Does anyone have the complete (barrel life) equation? </p><p></p><p></p><p>Yes, I do. I originated it on rec.guns years ago. And yes, it's </p><p>empirical. Over many years of competitive shooting, I learned from </p><p>all the top-scoring shooters their loads and rounds of accurate barrel </p><p>life. The key thing here is "accurate" barrel life by their </p><p>standards. In highpower competition, accurate barrel life ends when </p><p>shots missing where called by about 1/3rd more than when the barrel </p><p>was new and in its prime. In other words, when the barrel's grouping </p><p>ability is about 33% bigger. </p><p></p><p></p><p>The most common cartridge used until the mid 1960s was the .30-06 with </p><p>powder charges about 48 grains of powder. Top shooters would </p><p>typically rebarrel at about 3000 rounds; most would not enter the </p><p>Nationals with more than 1500 rounds through their current barrel. </p><p>Note that this number is based on shots at a rate of one per minute </p><p>for 10 to 20 minutes. For rapid fire at one shot every 6 seconds for </p><p>one minute, each of these rapid-fire shots is worth two of the </p><p>slow-fire ones. If lots of rapid fire is done, then naturally the </p><p>barrel life is shorter. I started looking at some fact about this </p><p>cartridge I could equate to its barrel life. It just happens than the </p><p>cross sectional area of a 30 caliber bore is about 48 square </p><p>millimeters (calculated with bullet diameter). It would seem that a </p><p>powder charge equaling 1 grain for each square millimeter of bore </p><p>cross sectional area means 3000 rounds of accurate barrel life. </p><p></p><p></p><p>Then I looked at other competition cartridges' barrel life as reported </p><p>by top scoring competitors: </p><p></p><p></p><p>.222 Rem.; 24 sq. mm, 21 grains, 4000 rounds. </p><p>.22 PPC; 24 sq. mm, 24 grains, 3000 rounds. </p><p>6mm PPC; 30 sq. mm, 28 grains, 3500 rounds. </p><p>.243 Win.; 30 sq. mm, 38 grains, 1600 rounds. </p><p>6.5x55 Swede; 35 sq. mm, 42 grains, 2000 rounds. </p><p>.264 Win. Mag.; 35 sq. mm, 72 grains, 600 rounds. </p><p>7mm-08; 41 sq. mm, 41 grains, 3000 rounds. </p><p>7mm Rem. Mag.; 41 sq. mm, 61 grains, 700 rounds. </p><p>.308 Win.; 41 sq. mm, 43 grains, 3500 rounds. </p><p>.30-.338 Mag.; 41 sq. mm, 65 grains, 1400 rounds. </p><p>.300 Win. Mag.; 41 sq. mm, 72 grains, 1000 rounds. </p><p>.300 Wby. Mag.; 41 sq. mm, 91 grains, 800 rounds. </p><p></p><p></p><p>This was a most interesting discovery. Cartridges using powder </p><p>charges equaling bore area (bore capacity?) got about 3000 rounds of </p><p>barrel life. Those using charges twice bore capacity got about </p><p>one-fourth of that or around 750 rounds. And those using less got </p><p>more than 3000 rounds. I've wondered where the term "over bore </p><p>capacity" came from; maybe this is why. </p><p></p><p></p><p>I did some trial-and-error math routines to come up with formulas to </p><p>plot a curve that fairly well tracked these numbers. Such empirical </p><p>processes have been used since the 1920s to calculate non-linear </p><p>ballistic cams used in military mechanical analog computers for aiming </p><p>large caliber guns with great accuracy results. So, I figured it </p><p>would work for this situation, too. </p><p></p><p></p><p>My formula is: </p><p>1. Calculate the bore area in square millimeters using bullet </p><p>diameter. </p><p>2. Use one grain of powder for each square millimeter. This is what I </p><p>call the reference, or bore capacity powder charge. Example: .30 </p><p>caliber bore, .308-in. (7.82 mm)bullet diameter = 48 square </p><p>millimeters. Bore capacity powder charge for .30 caliber is then 48 </p><p>grains. A .30 cal. cartridge that burns 48 grains of powder (.30-06) </p><p>gives a barrel life of about 3000 rounds of best accuracy. </p><p>3. If a larger 30 caliber cartridge is used and it burns more powder, </p><p>the accuracy life in rounds for that bore size is reduced. The amount </p><p>of reduction is determined by: </p><p>a. Divide the increased charge by the bore capacity, then square the </p><p>answer. </p><p>b. Divide that answer into 3000. Example: A .300 Wby Mag. has a bore </p><p>capacity of 48 grains. This cartridge burns 91 grains of powder. </p><p>(91/48) squared is 3.6. 3000 divided by 3.6 is 833 rounds. Three </p><p>competitive shooters told me their .300 Wby. rifles gave them between </p><p>800 and 900 rounds. </p><p></p><p></p><p>This also seems to work when using powder charges less than bore </p><p>capacity. The .222 Remington was the winning cartridge in benchrest </p><p>matches until the PPC family came along. It burned about 21 grains of </p><p>powder in a barrel whose bore capacity is about 24 grains. So, </p><p>(21/24) squared is 0.7656. 3000 divided by 0.7656 equals 3918 rounds. </p><p> Top benchresters in the '50s and '60s rebarreled their triple-deuce </p><p>stool guns at about 4000 rounds. </p><p></p><p></p><p>But this empirical formula has limits. The old .22 rimfire long rifle </p><p>burning 1 grain of powder in a bore whose capacity is 24 grains would </p><p>calculate to give a barrel life of some 1,728,000 rounds. But the top </p><p>international shooters I've talked to rebarrel their $4000 Anschutz </p><p>free rifles at about 25,000 rounds. And then there are thousands of </p><p>folks who claim a .22 rimfire barrel will never wear out. </p><p></p><p></p><p>And bore material and manufacturing processes can make a difference, </p><p>too. Most top-quality 30 caliber barrels get about 3000 accurate </p><p>rounds for the .308 Win. There's one make that gets about half that; </p><p>but they've been used to win the Nationals and other big highpower </p><p>matches more than once. </p><p></p><p></p><p>The intended firearm use and accuracy expectations comes to play, too. </p><p> Take the M1 and M14 service rifles. Their typical combat barrel life </p><p>established by arsenals is about 10,000 rounds with service ammo. </p><p>It's accuracy requirements was (as I remember) about 3.5 inches at 100 </p><p>yards. Compare this to top competitive highpower shooters </p><p>requirements of no more than 1/4th inch at 100 yards. That's what it </p><p>takes in highpower to stay under 1/3rd MOA at 200 yards, ½ MOA at 600 </p><p>yards and 3/4ths MOA at 1000 yards. </p><p></p><p></p><p>If anyone can shoot a hole through this theory, I welcome that shot. </p><p>This is more or less an emperical process based on accurate barrel </p><p>life in several calibers as reported to me by lots of folks plus a </p><p>couple dozen barrels I've worn out. All I did was study the data and </p><p>determine what math would give a best-fit formula. And if someone has </p><p>a better method, I'd like to know what it is. </p><p></p><p></p><p>And if your experience differs with this data, that's fine. Make your </p><p>own barrel life determinations based on what you observe using your </p><p>own accuracy standards. I don't expect everyone to have the same </p><p>standards, but it helps when they're realistic for the shooting </p><p>discipline. We all get to decide the most we want to miss where we </p><p>call the shot on the targets of our choice; animal (game &amp; varmints), </p><p>mineral (metallic silhouette) or vegetable (paper targets). </p><p></p><p>So According to this Fig Kirby your 7mm Allen Mag is as follows</p><p></p><p>7mm. 41 sq. mm, 118 grains </p><p>118/41 = 2.88 squared = 8.29 Then Didvide that bye 3000 = 362 rounds </p><p></p><p>Now just for [censored] and giggles lets figure the 122 grains that you say you can gain with it re-throated</p><p></p><p>7mm. 41 sq. mm, 122 grains </p><p>122/41 = 2.98 squared = 8.88/3000 = 337 Rounds Whew unless this formula is really jacked up ..That is a bbl SMOKER /ubbthreads/images/graemlins/shocked.gif Now before I get jumped...I know Kirby has his own figures on these Carts..His figs are for a sporter weight rifle use to 700 yards on deer size game..I believe his figures are about right + or - a few rounds <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite1" alt=":)" title="Smile :)" loading="lazy" data-shortname=":)" /></p><p>and as Kirby stated powder choice will play a big role in throat erosion Kiby I must say has takin all thse factors into consideration.. and designed these carts for optimum bbl life...Man I still want one Kirby..that 7mm Allen Mag has reall peaked my interest...AGAIN LOL!</p></blockquote><p></p>
[QUOTE="kac1345, post: 75182, member: 2172"] Ok Nobody string me up for this one lol! This is a Formula that seems to calculate accurate barrel life preety darn close YMMV. C/ Does anyone have the complete (barrel life) equation? Yes, I do. I originated it on rec.guns years ago. And yes, it's empirical. Over many years of competitive shooting, I learned from all the top-scoring shooters their loads and rounds of accurate barrel life. The key thing here is "accurate" barrel life by their standards. In highpower competition, accurate barrel life ends when shots missing where called by about 1/3rd more than when the barrel was new and in its prime. In other words, when the barrel's grouping ability is about 33% bigger. The most common cartridge used until the mid 1960s was the .30-06 with powder charges about 48 grains of powder. Top shooters would typically rebarrel at about 3000 rounds; most would not enter the Nationals with more than 1500 rounds through their current barrel. Note that this number is based on shots at a rate of one per minute for 10 to 20 minutes. For rapid fire at one shot every 6 seconds for one minute, each of these rapid-fire shots is worth two of the slow-fire ones. If lots of rapid fire is done, then naturally the barrel life is shorter. I started looking at some fact about this cartridge I could equate to its barrel life. It just happens than the cross sectional area of a 30 caliber bore is about 48 square millimeters (calculated with bullet diameter). It would seem that a powder charge equaling 1 grain for each square millimeter of bore cross sectional area means 3000 rounds of accurate barrel life. Then I looked at other competition cartridges' barrel life as reported by top scoring competitors: .222 Rem.; 24 sq. mm, 21 grains, 4000 rounds. .22 PPC; 24 sq. mm, 24 grains, 3000 rounds. 6mm PPC; 30 sq. mm, 28 grains, 3500 rounds. .243 Win.; 30 sq. mm, 38 grains, 1600 rounds. 6.5x55 Swede; 35 sq. mm, 42 grains, 2000 rounds. .264 Win. Mag.; 35 sq. mm, 72 grains, 600 rounds. 7mm-08; 41 sq. mm, 41 grains, 3000 rounds. 7mm Rem. Mag.; 41 sq. mm, 61 grains, 700 rounds. .308 Win.; 41 sq. mm, 43 grains, 3500 rounds. .30-.338 Mag.; 41 sq. mm, 65 grains, 1400 rounds. .300 Win. Mag.; 41 sq. mm, 72 grains, 1000 rounds. .300 Wby. Mag.; 41 sq. mm, 91 grains, 800 rounds. This was a most interesting discovery. Cartridges using powder charges equaling bore area (bore capacity?) got about 3000 rounds of barrel life. Those using charges twice bore capacity got about one-fourth of that or around 750 rounds. And those using less got more than 3000 rounds. I've wondered where the term "over bore capacity" came from; maybe this is why. I did some trial-and-error math routines to come up with formulas to plot a curve that fairly well tracked these numbers. Such empirical processes have been used since the 1920s to calculate non-linear ballistic cams used in military mechanical analog computers for aiming large caliber guns with great accuracy results. So, I figured it would work for this situation, too. My formula is: 1. Calculate the bore area in square millimeters using bullet diameter. 2. Use one grain of powder for each square millimeter. This is what I call the reference, or bore capacity powder charge. Example: .30 caliber bore, .308-in. (7.82 mm)bullet diameter = 48 square millimeters. Bore capacity powder charge for .30 caliber is then 48 grains. A .30 cal. cartridge that burns 48 grains of powder (.30-06) gives a barrel life of about 3000 rounds of best accuracy. 3. If a larger 30 caliber cartridge is used and it burns more powder, the accuracy life in rounds for that bore size is reduced. The amount of reduction is determined by: a. Divide the increased charge by the bore capacity, then square the answer. b. Divide that answer into 3000. Example: A .300 Wby Mag. has a bore capacity of 48 grains. This cartridge burns 91 grains of powder. (91/48) squared is 3.6. 3000 divided by 3.6 is 833 rounds. Three competitive shooters told me their .300 Wby. rifles gave them between 800 and 900 rounds. This also seems to work when using powder charges less than bore capacity. The .222 Remington was the winning cartridge in benchrest matches until the PPC family came along. It burned about 21 grains of powder in a barrel whose bore capacity is about 24 grains. So, (21/24) squared is 0.7656. 3000 divided by 0.7656 equals 3918 rounds. Top benchresters in the ‘50s and ‘60s rebarreled their triple-deuce stool guns at about 4000 rounds. But this empirical formula has limits. The old .22 rimfire long rifle burning 1 grain of powder in a bore whose capacity is 24 grains would calculate to give a barrel life of some 1,728,000 rounds. But the top international shooters I've talked to rebarrel their $4000 Anschutz free rifles at about 25,000 rounds. And then there are thousands of folks who claim a .22 rimfire barrel will never wear out. And bore material and manufacturing processes can make a difference, too. Most top-quality 30 caliber barrels get about 3000 accurate rounds for the .308 Win. There's one make that gets about half that; but they've been used to win the Nationals and other big highpower matches more than once. The intended firearm use and accuracy expectations comes to play, too. Take the M1 and M14 service rifles. Their typical combat barrel life established by arsenals is about 10,000 rounds with service ammo. It's accuracy requirements was (as I remember) about 3.5 inches at 100 yards. Compare this to top competitive highpower shooters requirements of no more than 1/4th inch at 100 yards. That's what it takes in highpower to stay under 1/3rd MOA at 200 yards, ½ MOA at 600 yards and 3/4ths MOA at 1000 yards. If anyone can shoot a hole through this theory, I welcome that shot. This is more or less an emperical process based on accurate barrel life in several calibers as reported to me by lots of folks plus a couple dozen barrels I've worn out. All I did was study the data and determine what math would give a best-fit formula. And if someone has a better method, I'd like to know what it is. And if your experience differs with this data, that's fine. Make your own barrel life determinations based on what you observe using your own accuracy standards. I don't expect everyone to have the same standards, but it helps when they're realistic for the shooting discipline. We all get to decide the most we want to miss where we call the shot on the targets of our choice; animal (game & varmints), mineral (metallic silhouette) or vegetable (paper targets). So According to this Fig Kirby your 7mm Allen Mag is as follows 7mm. 41 sq. mm, 118 grains 118/41 = 2.88 squared = 8.29 Then Didvide that bye 3000 = 362 rounds Now just for [censored] and giggles lets figure the 122 grains that you say you can gain with it re-throated 7mm. 41 sq. mm, 122 grains 122/41 = 2.98 squared = 8.88/3000 = 337 Rounds Whew unless this formula is really jacked up ..That is a bbl SMOKER [img]/ubbthreads/images/graemlins/shocked.gif[/img] Now before I get jumped...I know Kirby has his own figures on these Carts..His figs are for a sporter weight rifle use to 700 yards on deer size game..I believe his figures are about right + or - a few rounds :-) and as Kirby stated powder choice will play a big role in throat erosion Kiby I must say has takin all thse factors into consideration.. and designed these carts for optimum bbl life...Man I still want one Kirby..that 7mm Allen Mag has reall peaked my interest...AGAIN LOL! [/QUOTE]
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