Rather than resuscitating one of the three many-years-old threads mentioned in yesterday's article on "Magazine Management," I am instead creating a new thread, as I would like to introduce some basic engineering fundamentals of springs up front, so that the discussion at least begins on a scientifically-verifiable footing while avoiding both the confusion and misinformation that appears to have plagued those previous threads.
First, let's talk about the material used in our magazines: "Spring steel is a name given to a wide range of steels used in the manufacture of springs, prominently in automotive and industrial suspension applications. These steels are generally low-alloy Manganese, medium-carbon steel or high-carbon steel with a very high yield strength. This allows objects made of spring steel to return to their original shape despite significant deflection or twisting." - Wikipedia
Now, the article had me a little confused.* I was confused because the conclusions reached by its author did not jibe with what I have learned, either while studying engineering or as a manufacturing engineer dealing with springs. LOTS of springs. I'm sure the author meant well, but it's obvious he doesn't understand the physics behind the phenomenon for two reasons. First, he failed to use the correct term, "creep," to the describe what can happen under some circumstances when you compress and hold a spring for a long time. Second, he incorrectly used a related term, "set," in the wrong context.
Thus, if you will, I'd like to set the record straight:
Springs may experience two types of deformation:
Set: Set is a permanent and immediate deformation that happens within the first few cycles of spring compression after manufacture. Set is permanent, but can be compensated for during manufacture simply by planning for set and producing a spring that's too long, initially, (or too short if the spring is under tension) but one that will set to designed length after those first few cycles. Whether or not a spring even experiences set depends on the level of stress a spring undergoes during design use as compared to the material's tensile strength:
- spring is compressed from 0%-40% of its tensile strength: No appreciable set occurs
- spring is compressed between 40%-60% of tensile strength: The set can be compensated for during manufacturing
- spring is compressed more than 60% of its tensile strength: The set cannot be controlled
The obvious learning point here is to design magazine springs such that if they do exceed 40% of their tensile strength, they never exceed 60% and the set is predicted and accounted for during manufacturing such that after initial use, the spring sets at design specifications.
Contrary to the author's misstatement, set is not what occurs when you leave rounds in a magazine for a long period of time.* That phenomenon is called "creep."**Furthermore, "fatigue" is something altogether different, having to do with cyclical stress. Thus, the author's comment that "Many argue that you need to rotate magazines at least every few months so that springs don’t fatigue and take a set" is meaningless, as fatigue causes neither set nor creep.
This mismatch of terms and misunderstanding of the differences between these three phenomena is actually quite common, hence the need for this post.
Creep: Creep is usually what people talk about when they think about keeping rounds in a magazine. Creep occurs under constant load over time. It is a plastic deformation at some stress below the yield stress that occurs very slowly over time. Technically, it's called creep when a spring under constant load loses length and it is called relaxation when a spring under constant compression loses load.
The greatest factors affecting creep are temperature and % stress levels. Not surprisingly, cyclical fatigue can increase creep. However, if the spring is kept below 60% of its tensile strength, the number of cycles achieved before breakage can actually exceed 10 million. And below 40% of tensile strength, creep ceases being a factor at any temperature where firearms are apt to be stored or employed.
Fatigue is what occurs when you cycle a part in and out of stress. You can avoid fatigue altogether by keeping the design stress well below the maximum stress. Generally speaking, when the designed stress is less than 60% of the maximum limit of elastic deformation, fatigue never occurs, and your cycle count before failure approaches infinity. To really put things into perspective, consider a steel valve spring, which operates in temperatures around 200 degrees Fahrenheit. They undergo one compression cycle for every two cycles of the engine. If the engine operates at 2,200 RPM, that's 1,100 compressions per minute (or mile, at highway speeds). At 100,000 miles, that's 110,000,000 (110 Million) compressions for your average engine . They achieve that by keeping compression to roughly 50% of the tensile strength.
The same thing goes for modern weapons. Any modern, well-designed arm is made with magazine springs that will not suffer from either any appreciable amount of creep or stress throughout it's lifetime wear limits. Thus, the whole rather retentive business about which magazines to use when, which are loaded or not, and rotating them six months on and six months off, becomes a meaningless if not rather tedious exercise for modern, high-quality magazines from reputable firearms manufacturers.
Having said all that, the older your magazine, the more likely it was designed without this now-common knowledge, and the more likely its spring may have suffered some creep.
Even so, many well-designed older firearms were free from this problem. In fact, I just got off the phone with a 76-year-old friend of mine who owns a 1914 artillery Luger. He acquired it in the late 1950s, and told me after he let a gunsmith give it a thorough inspection in 1958, which resulted in a "perfect working order" report without anything more than a cleaning, my friend has fired it on numerous occasions and has used it as his primary "pillow weapon" ever since, with rounds in the chamber without letup for nearly 60 years as determined by occasional tests with perfect feeds at the firing range. Result: No creep at all.
Bottom line: While the author does provide some interesting considerations for "storing magazines in accessible locations," if your firearm was made in the last couple of decades by a reputable manufacturer, you can save yourself a lot of unnecessarily wasted time and trouble swapping out magazines while actually being more prepared by simply keeping those puppies loaded.
On a related note, using brand new magazines as primary isn't too smart, but you don't want to use ones that have seen 100,000 rounds, either. Thus, just use "seasoned" (couple hundred to a couple of thousand rounds) magazines as primary, fairly new (but still tested and broken in) magazines as secondary, and your oldest magazines as tertiary.
Finally, here's how I approach the issue:
1. My two best seasoned magazines appear in my firearm and the spare pouch that's part of my holster. I carry that with me whenever I can.
2. My two newer, but still broken in magazines appear in my my leather belt pouch that I sometimes wear in higher threat areas.
3. My additional, older magazines, along with a couple hundred loose rounds, appear in my thick canvas ammo bag I sometimes carry with me on trips.
All of my magazines were manufactured by a well-known and highly reputable firearms company within the last decade. Thus, I keep all magazines loaded at all times, except while shooting or cleaning them.
To be quite frank, as an engineer with an abundance of experience involving the design, employment and use of springs, I am far more concerned about wear at the point where the magazine is retained or the exit point from which the rounds are fed than about their springs.
Undoubtedly, someone will send me pictures of a failed modern magazine spring. Don't be surprised if I send you pictures of failed modern airliners into which infinitely more time, effort, and money was poured to avoid any sort of failure. Single events, or even a small collection of failures do not establish any sort of trend when examined alongside tens of millions of successes. They are statistical outliers, anecdotal evidence at best, and very few and far between.
One last bit of insight, in the form of a thought experiment:
On my 16-round magazines, the design minimum spring compression occurs with just 1 round in the chamber, but with a 3x factor of safety. Thus, the spring only needs to push one-third as hard as it normally pushes in order for that last round to feed. Let's call this a force of 1. Thus, the actual push is with a force of 3. Simultaneously, at full compression the spring is still at just 30% of its designed maximum stress.
Given the physical dimensions, we calculate that the maximum force is 2.95 x the minimum force, or 30% of the maximum stress of the spring, whereas the minimum (no rounds) compression is still 9.73% of the maximum stress of the spring. The unloaded stress is about a third of the loaded stress.
Funny how that works.
Also, you achieve an 11.5% reduction in spring compression simply by removing one bullet from the stack of 16.
I could play with numbers all night long, but it's late, so I'm hitting the hay.
First, let's talk about the material used in our magazines: "Spring steel is a name given to a wide range of steels used in the manufacture of springs, prominently in automotive and industrial suspension applications. These steels are generally low-alloy Manganese, medium-carbon steel or high-carbon steel with a very high yield strength. This allows objects made of spring steel to return to their original shape despite significant deflection or twisting." - Wikipedia
Now, the article had me a little confused.* I was confused because the conclusions reached by its author did not jibe with what I have learned, either while studying engineering or as a manufacturing engineer dealing with springs. LOTS of springs. I'm sure the author meant well, but it's obvious he doesn't understand the physics behind the phenomenon for two reasons. First, he failed to use the correct term, "creep," to the describe what can happen under some circumstances when you compress and hold a spring for a long time. Second, he incorrectly used a related term, "set," in the wrong context.
Thus, if you will, I'd like to set the record straight:
Springs may experience two types of deformation:
Set: Set is a permanent and immediate deformation that happens within the first few cycles of spring compression after manufacture. Set is permanent, but can be compensated for during manufacture simply by planning for set and producing a spring that's too long, initially, (or too short if the spring is under tension) but one that will set to designed length after those first few cycles. Whether or not a spring even experiences set depends on the level of stress a spring undergoes during design use as compared to the material's tensile strength:
- spring is compressed from 0%-40% of its tensile strength: No appreciable set occurs
- spring is compressed between 40%-60% of tensile strength: The set can be compensated for during manufacturing
- spring is compressed more than 60% of its tensile strength: The set cannot be controlled
The obvious learning point here is to design magazine springs such that if they do exceed 40% of their tensile strength, they never exceed 60% and the set is predicted and accounted for during manufacturing such that after initial use, the spring sets at design specifications.
Contrary to the author's misstatement, set is not what occurs when you leave rounds in a magazine for a long period of time.* That phenomenon is called "creep."**Furthermore, "fatigue" is something altogether different, having to do with cyclical stress. Thus, the author's comment that "Many argue that you need to rotate magazines at least every few months so that springs don’t fatigue and take a set" is meaningless, as fatigue causes neither set nor creep.
This mismatch of terms and misunderstanding of the differences between these three phenomena is actually quite common, hence the need for this post.
Creep: Creep is usually what people talk about when they think about keeping rounds in a magazine. Creep occurs under constant load over time. It is a plastic deformation at some stress below the yield stress that occurs very slowly over time. Technically, it's called creep when a spring under constant load loses length and it is called relaxation when a spring under constant compression loses load.
The greatest factors affecting creep are temperature and % stress levels. Not surprisingly, cyclical fatigue can increase creep. However, if the spring is kept below 60% of its tensile strength, the number of cycles achieved before breakage can actually exceed 10 million. And below 40% of tensile strength, creep ceases being a factor at any temperature where firearms are apt to be stored or employed.
Fatigue is what occurs when you cycle a part in and out of stress. You can avoid fatigue altogether by keeping the design stress well below the maximum stress. Generally speaking, when the designed stress is less than 60% of the maximum limit of elastic deformation, fatigue never occurs, and your cycle count before failure approaches infinity. To really put things into perspective, consider a steel valve spring, which operates in temperatures around 200 degrees Fahrenheit. They undergo one compression cycle for every two cycles of the engine. If the engine operates at 2,200 RPM, that's 1,100 compressions per minute (or mile, at highway speeds). At 100,000 miles, that's 110,000,000 (110 Million) compressions for your average engine . They achieve that by keeping compression to roughly 50% of the tensile strength.
The same thing goes for modern weapons. Any modern, well-designed arm is made with magazine springs that will not suffer from either any appreciable amount of creep or stress throughout it's lifetime wear limits. Thus, the whole rather retentive business about which magazines to use when, which are loaded or not, and rotating them six months on and six months off, becomes a meaningless if not rather tedious exercise for modern, high-quality magazines from reputable firearms manufacturers.
Having said all that, the older your magazine, the more likely it was designed without this now-common knowledge, and the more likely its spring may have suffered some creep.
Even so, many well-designed older firearms were free from this problem. In fact, I just got off the phone with a 76-year-old friend of mine who owns a 1914 artillery Luger. He acquired it in the late 1950s, and told me after he let a gunsmith give it a thorough inspection in 1958, which resulted in a "perfect working order" report without anything more than a cleaning, my friend has fired it on numerous occasions and has used it as his primary "pillow weapon" ever since, with rounds in the chamber without letup for nearly 60 years as determined by occasional tests with perfect feeds at the firing range. Result: No creep at all.
Bottom line: While the author does provide some interesting considerations for "storing magazines in accessible locations," if your firearm was made in the last couple of decades by a reputable manufacturer, you can save yourself a lot of unnecessarily wasted time and trouble swapping out magazines while actually being more prepared by simply keeping those puppies loaded.
On a related note, using brand new magazines as primary isn't too smart, but you don't want to use ones that have seen 100,000 rounds, either. Thus, just use "seasoned" (couple hundred to a couple of thousand rounds) magazines as primary, fairly new (but still tested and broken in) magazines as secondary, and your oldest magazines as tertiary.
Finally, here's how I approach the issue:
1. My two best seasoned magazines appear in my firearm and the spare pouch that's part of my holster. I carry that with me whenever I can.
2. My two newer, but still broken in magazines appear in my my leather belt pouch that I sometimes wear in higher threat areas.
3. My additional, older magazines, along with a couple hundred loose rounds, appear in my thick canvas ammo bag I sometimes carry with me on trips.
All of my magazines were manufactured by a well-known and highly reputable firearms company within the last decade. Thus, I keep all magazines loaded at all times, except while shooting or cleaning them.
To be quite frank, as an engineer with an abundance of experience involving the design, employment and use of springs, I am far more concerned about wear at the point where the magazine is retained or the exit point from which the rounds are fed than about their springs.
Undoubtedly, someone will send me pictures of a failed modern magazine spring. Don't be surprised if I send you pictures of failed modern airliners into which infinitely more time, effort, and money was poured to avoid any sort of failure. Single events, or even a small collection of failures do not establish any sort of trend when examined alongside tens of millions of successes. They are statistical outliers, anecdotal evidence at best, and very few and far between.
One last bit of insight, in the form of a thought experiment:
On my 16-round magazines, the design minimum spring compression occurs with just 1 round in the chamber, but with a 3x factor of safety. Thus, the spring only needs to push one-third as hard as it normally pushes in order for that last round to feed. Let's call this a force of 1. Thus, the actual push is with a force of 3. Simultaneously, at full compression the spring is still at just 30% of its designed maximum stress.
Given the physical dimensions, we calculate that the maximum force is 2.95 x the minimum force, or 30% of the maximum stress of the spring, whereas the minimum (no rounds) compression is still 9.73% of the maximum stress of the spring. The unloaded stress is about a third of the loaded stress.
Funny how that works.
Also, you achieve an 11.5% reduction in spring compression simply by removing one bullet from the stack of 16.
I could play with numbers all night long, but it's late, so I'm hitting the hay.
