On Magazines and spring fatigue/failure

[ryan3030]

*edit* Disclaimer: I did not create this, just passing it on.

 

[charley59]

Good reading. Explains a lot. Good magazine springs, properly engineered for the application, that are not corroded, will not fail. Loading and unloading is more stressful on the spring than keeping the magazine loaded.

 

[LarryC]

Pretty common sense if you think about it, many springs such as automobile, truck, even light switches are left in a loaded state for many years without any failure issues. I leave magazines loaded for SKS, AK and my 45 colt and have for several years with no issues.

 

[jaybird_123]

Great article, thank you. I am more at ease now. Thanks.

 

[CountryBoy19]

I mostly agree, however I disagree with him about fatigue. Springs do fatigue and he implies that they don't fatigue enough to matter until you get into the range of millions of cycles.

However, that isn't the case. As his chart shows, the fatigue life is dependent on the stress in the spring. He is assuming that mag springs etc are designed perfectly so that the stress level is very, very low. But that isn't the case. Without going too deep into engineering, the stress level is relatively proportional to the magazine force. To get the same force but with less stress on the material you have to go with a more "powerful spring" but flex it less. So to get a very, very low stress level we also need a very, very over-powered spring that we only flex a very small amount. That isn't the case, we use springs that balance between spring design and cyclical life. I can say with absolute certainty that you won't reliably get 1,000,000+ cycles out of any magazine spring without feeding problems. With each cycle the spring fatigues and yields less return force, and this will eventually drop to the point that the force is not enough to reliably feed the ammunition.

Just for example, I've worn out recoil springs in handguns to the point that they wouldn't reliably cycle and I sure didn't put 1,000,000+ rounds through the gun. Likewise, magazine springs will be similar in nature. The cyclic life is dependent on the actual stress level in the spring and a well designed spring will utilize a large portion of the range of stress in the elastic region.

ETA, just to clarify my comments regard over-power springs and same stress etc imagine this. You have 2 different springs. 1 is the compression spring from a ball-point pen and 1 is from the front shock tower of a 1-ton dodge pickup truck. You put a 6 oz weight on each. The ball-point pen spring collapses almost all the way and the internal stress is the spring is quite high. Mean-while the spring from the Dodge truck didn't even compress noticeably. It did compress though, and it is now providing a 6 oz return force. Which spring will last longer? The one from the truck will because the internal stress is much, much lower and it will therefore last well into that million+ cycle range. The same can't be said for ink-pen spring though. So if you want a mag-spring to last into the million+ cycle range you're going to have to make it big, heavy, and much longer than the magazine to get to that point. I hope that isn't too confusing.

I just wanted to add in the part that the author of that paper neglected to mention.

 

[MbMinx]

It's good to hear that leaving my magazines at least partially loaded will probably not cause significant damage to my mag springs.
Since cleaning out my Dad's closet and finding random, unidentified magazines just stuck anywhere, I want to store at least a couple of cartridges in each of mine in case they were to accidentally get separated from the gun. That way I'd know which mag goes to which gun.

 

[Never A Victim]

Good read.

 

[ryan3030]

It's good to hear that leaving my magazines at least partially loaded will probably not cause significant damage to my mag springs.
Since cleaning out my Dad's closet and finding random, unidentified magazines just stuck anywhere, I want to store at least a couple of cartridges in each of mine in case they were to accidentally get separated from the gun. That way I'd know which mag goes to which gun.

Paint or colored tape on the baseplate can help with that.

 

[U.S. Patriot]

I'm having issues with the mags that are loaded and kept in my FNP. I have had to stretch them a couple of times. Now I have to see if I can find replacements.

 

[ryan3030]

I'm having issues with the mags that are loaded and kept in my FNP. I have had to stretch them a couple of times. Now I have to see if I can find replacements.

Sounds like poor quality springs.

 

[U.S. Patriot]

Sounds like poor quality springs.

I agree, I have not had issues with any other mags for other firearms. I'm going to contact FN.