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Posted: 4/22/2020 3:28:05 PM EDT
6.5 creedmoor barrel life is less than 308, generally? Why? They're about the same velocity. Is it that the burning powder is concentrated on less surface area; internal circumference of the 6.5 barrel is less?
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Smaller barrel hole with equal case size means more hot gas to erode barrel as it exits.
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Originally Posted By boltedsafe: Smaller barrel hole with equal case size means more hot gas to erode barrel as it exits. View Quote Yep, its all about the amount of powder versus the size of the area it can escape thru...more powder/smaller hole = more/faster wear....now think 6.5 Creedmoor versus 6.5PRC.... Slowing down the rate of fire, so the barrel doesn't get as hot can make a drastic difference in throat life... |
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I think it has to do with P=F/A. Keep the relatively same powder charge (F) and start shrinking down the tube (A) and P is going to start going up pretty quick resulting in moar erosion. I have no idea though honestly just a thought I had one day after doing some formulas at work.
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Put a 1" pipe in your mouth and blow as hard as you can.
Then put a coffee straw in your mouth and blow as hard as you can. After you wake up from passing put you will understand something new about physics. |
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Fundamentally the marksman aims at himself.
— D.T. Suzuki |
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A more interesting part of the question is, "why do we give 6.5CM a hard time about barrel life when the only caliber in the genre that beats it is the 308, which really ISN'T in the same genre, but is just a traditional comparison point people understand.
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Is the 308 really running similar speeds? I know reducing the bore size increases pressure but I have never seen anyone really break down barrel wear as far as Pressure vs velocity vs bullet material etc. I've always been under the impression velocity is usually the biggest factor as people using the same caliber can have drastically different barrel life just by adjusting their speed. I also know that some powders are especially harsh and can cause erosion all by themselves.
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BikerNut:
Normal people like motorcycles. Real people like motorcycles. People who don't like motorcycles are just... weird. |
I have a 6mm Creedmoor as well as a 6.5. I don't shoot long strings out of the 6 I'm sure if I did the barrel would be toast in short order. Of course barrels are consumables.
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Originally Posted By ALASKANFIRE: Is the 308 really running similar speeds? I know reducing the bore size increases pressure but I have never seen anyone really break down barrel wear as far as Pressure vs velocity vs bullet material etc. I've always been under the impression velocity is usually the biggest factor as people using the same caliber can have drastically different barrel life just by adjusting their speed. I also know that some powders are especially harsh and can cause erosion all by themselves. View Quote 140-150gr bullet at ~2800fps. |
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Distinguished Rifleman #2223
"Technique isn't something that can be taught. It's something you find on your own." - Bunta Fujiwara |
Originally Posted By HighpowerRifleBrony: 140-150gr bullet at ~2800fps. View Quote View All Quotes View All Quotes Originally Posted By HighpowerRifleBrony: Originally Posted By ALASKANFIRE: Is the 308 really running similar speeds? I know reducing the bore size increases pressure but I have never seen anyone really break down barrel wear as far as Pressure vs velocity vs bullet material etc. I've always been under the impression velocity is usually the biggest factor as people using the same caliber can have drastically different barrel life just by adjusting their speed. I also know that some powders are especially harsh and can cause erosion all by themselves. 140-150gr bullet at ~2800fps. It's been a while but aren't most 308 175 loads only around 2600? I am aware they can be loaded hotter but I was under the impression similar class bullets were 10-15% faster in the 6.5. |
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BikerNut:
Normal people like motorcycles. Real people like motorcycles. People who don't like motorcycles are just... weird. |
Originally Posted By ALASKANFIRE: It's been a while but aren't most 308 175 loads only around 2600? I am aware they can be loaded hotter but I was under the impression similar class bullets were 10-15% faster in the 6.5. View Quote Comparing bullet weight only, not bullet form. A quick search shows 24" barrels launching M80 (146-150gr?) at about 2800fps, and 140-147gr CM loads in the 2700s. As I see it, the pressure limit encourages slower powders which makes a longer burn time, combined with the similar weight charge being concentrated into a smaller hole. Without the same bore volume, the CM is about as efficient powder wise, just trading higher BC bullets for barrel life. |
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Distinguished Rifleman #2223
"Technique isn't something that can be taught. It's something you find on your own." - Bunta Fujiwara |
Originally Posted By HighpowerRifleBrony: Comparing bullet weight only, not bullet form. A quick search shows 24" barrels launching M80 (146-150gr?) at about 2800fps, and 140-147gr CM loads in the 2700s. As I see it, the pressure limit encourages slower powders which makes a longer burn time, combined with the similar weight charge being concentrated into a smaller hole. Without the same bore volume, the CM is about as efficient powder wise, just trading higher BC bullets for barrel life. View Quote I kinda wonder if increased surface area of the higher BC bullets helps decrease barrel life with the slower powders? I have wondered if the heavies in the .308 decreased barrel life compared the old standard 168's? I was shooting 190 gr bullets 30 years ago and had to set my barrel back at around 2800 rounds due to throat erosion with ball powders BLC-2 and win 748. I am willing to bet if you ran a Ball powder in the Creed's it would reduce throat life faster than the slower extruded powders? |
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Chicken Farmer by choice hunter of shade tree's and hiding spots by nature.
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Originally Posted By sparkyD: I kinda wonder if increased surface area of the higher BC bullets helps decrease barrel life with the slower powders? I have wondered if the heavies in the .308 decreased barrel life compared the old standard 168's? I was shooting 190 gr bullets 30 years ago and had to set my barrel back at around 2800 rounds due to throat erosion with ball powders BLC-2 and win 748. I am willing to bet if you ran a Ball powder in the Creed's it would reduce throat life faster than the slower extruded powders? View Quote View All Quotes View All Quotes Originally Posted By sparkyD: Originally Posted By HighpowerRifleBrony: Comparing bullet weight only, not bullet form. A quick search shows 24" barrels launching M80 (146-150gr?) at about 2800fps, and 140-147gr CM loads in the 2700s. As I see it, the pressure limit encourages slower powders which makes a longer burn time, combined with the similar weight charge being concentrated into a smaller hole. Without the same bore volume, the CM is about as efficient powder wise, just trading higher BC bullets for barrel life. I kinda wonder if increased surface area of the higher BC bullets helps decrease barrel life with the slower powders? I have wondered if the heavies in the .308 decreased barrel life compared the old standard 168's? I was shooting 190 gr bullets 30 years ago and had to set my barrel back at around 2800 rounds due to throat erosion with ball powders BLC-2 and win 748. I am willing to bet if you ran a Ball powder in the Creed's it would reduce throat life faster than the slower extruded powders? One thing that doesn't seem to help is that in the real world most of the people loading the super heavies are also loading at the max end of the spectrum at least in my experience. |
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BikerNut:
Normal people like motorcycles. Real people like motorcycles. People who don't like motorcycles are just... weird. |
Originally Posted By ALASKANFIRE: One thing that doesn't seem to help is that in the real world most of the people loading the super heavies are also loading at the max end of the spectrum at least in my experience. View Quote Yes Sir! But at least now we have some really excellent bullets compared to thirty years ago. Just the improvement in jacket material alone has been phenomenal. I can remember the first Bergers hitting the seen and Sierra playing catch up and Hornady completely dropping their 190gr bullet. |
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Chicken Farmer by choice hunter of shade tree's and hiding spots by nature.
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For reference, I shoot 155’s at about 3030 fps in my .308’s, and generally take them off at about 3500 rounds. Every one of them has still been shooting great at that number, but I don’t like to push my luck for anything important. For the sake of science, I decided to keep shooting last year’s Krieger for practice and small matches to see how long it would last. At 4100, it was about the best shooting 308 barrel I’ve ever had. At 4400, it was toast. That experiment reinforced my belief that 3500 is a good number for replacement.
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On the day shift at the Utility Muffin Research Kitchen
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Originally Posted By erud: For reference, I shoot 155’s at about 3030 fps in my .308’s, and generally take them off at about 3500 rounds. Every one of them has still been shooting great at that number, but I don’t like to push my luck for anything important. For the sake of science, I decided to keep shooting last year’s Krieger for practice and small matches to see how long it would last. At 4100, it was about the best shooting 308 barrel I’ve ever had. At 4400, it was toast. That experiment reinforced my belief that 3500 is a good number for replacement. View Quote Did you notice after about 3500 your case neck building carbon a lot faster? |
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Chicken Farmer by choice hunter of shade tree's and hiding spots by nature.
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Originally Posted By sparkyD: Did you notice after about 3500 your case neck building carbon a lot faster? View Quote I’m not exactly sure what you mean by that. Difference in the amount of carbon soot on the case neck after firing? I did not notice anything like that, let me know if you are referring to something else. |
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On the day shift at the Utility Muffin Research Kitchen
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Originally Posted By erud: For reference, I shoot 155's at about 3030 fps in my .308's, and generally take them off at about 3500 rounds. Every one of them has still been shooting great at that number, but I don't like to push my luck for anything important. For the sake of science, I decided to keep shooting last year's Krieger for practice and small matches to see how long it would last. At 4100, it was about the best shooting 308 barrel I've ever had. At 4400, it was toast. That experiment reinforced my belief that 3500 is a good number for replacement. View Quote What is toast to you? |
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Distinguished Rifleman #2223
"Technique isn't something that can be taught. It's something you find on your own." - Bunta Fujiwara |
Originally Posted By HighpowerRifleBrony: 30 or 32"? What is toast to you? View Quote I shoot 30" 12 or 13 twist, that particular Krieger was a 13. At 4100 rounds it shot a 798-61x in a 4x600 match, so just over 75% x-count. 2 weeks later at an 8x600 it shot 1590-91 X, so about 57%. I was getting skeptical at that point. Next 4x600 was 784-30x, or about 38%. Worst Mid Range score I have shot in about 10 years. Similar conditions at all 3 matches, and I know what kind of scores I expect to shoot. The drop-off in accuracy was very dramatic, it was definitely enough evidence to convince me that 3500 is indeed a good number. |
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On the day shift at the Utility Muffin Research Kitchen
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Originally Posted By erud: I’m not exactly sure what you mean by that. Difference in the amount of carbon soot on the case neck after firing? I did not notice anything like that, let me know if you are referring to something else. View Quote Yeah around the neck and shoulder area. My buddy his .308 did that but mine launching the 190's didn't. I thought it might have been due to the 150-168's he was shooting having a bit more velocity with a shorter pressure curve than the 190's with their more surface area creating a longer pressure curve. But then again he had a custom chamber vs my factory chamber in my 700. |
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Chicken Farmer by choice hunter of shade tree's and hiding spots by nature.
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Originally Posted By sparkyD: Yeah around the neck and shoulder area. My buddy his .308 did that but mine launching the 190's didn't. I thought it might have been due to the 150-168's he was shooting having a bit more velocity with a shorter pressure curve than the 190's with their more surface area creating a longer pressure curve. But then again he had a custom chamber vs my factory chamber in my 700. View Quote View All Quotes View All Quotes Originally Posted By sparkyD: Originally Posted By erud: I’m not exactly sure what you mean by that. Difference in the amount of carbon soot on the case neck after firing? I did not notice anything like that, let me know if you are referring to something else. Yeah around the neck and shoulder area. My buddy his .308 did that but mine launching the 190's didn't. I thought it might have been due to the 150-168's he was shooting having a bit more velocity with a shorter pressure curve than the 190's with their more surface area creating a longer pressure curve. But then again he had a custom chamber vs my factory chamber in my 700. I didn't notice anything unusual in that regard. Mine are all chambered with a 2011 Fullbore reamer. |
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On the day shift at the Utility Muffin Research Kitchen
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Originally Posted By WI_Bill: 6.5 creedmoor barrel life is less than 308, generally? Why? They're about the same velocity. Is it that the burning powder is concentrated on less surface area; internal circumference of the 6.5 barrel is less? View Quote |
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dQ / (dA * dt) = more erosion on smaller bore
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