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Bubacus
May 11, 2015, 05:57
I guess those cheap Polish mags weren't quite the bargin the writer was hoping for. He believed they were Bulgarian, someone else comments below points out they are actually Polish:

http://thegunwriter.blogs.heraldtribune.com/19338/im-done-with-polymer-ak-mags/

http://thegunwriter.blogs.heraldtribune.com/files/2015/04/AKMag-004-1024x768.jpg

I’m done with polymer AK mags

Posted on April 30, 2015 by Lee Williams

I had a surprise last night when I opened my safe.


The top of a loaded polymer AK mag had broken off for reasons unknown, spraying 28 loaded rounds and bits of plastic all over my safe.

The spring was sticking halfway out of the top of the mag. I found the follower behind an SKS.

To be clear, the mag was not in a rifle. It was one of several loaded mags I keep on a shelf of the safe.

The offender was a Bulgarian slab-side polymer magazine, which is usually considered one of the better mil-spec-type AK magazines

It hadn’t been loaded for that long, maybe a couple weeks. I rotate my magazines between trips to the range to give the springs a break. And as I said, it was loaded with 28 rounds, not 30.

The lesson I learned: The best AK mags are still the Combloc steel.

They’re a bit heavier, but the extra durability makes them well worth it. You can nearly play hockey with a steel AK mag without worry. They’re also easier to pull out of a chest rig than the waffle-sided variety.

Tuhlmann
May 11, 2015, 06:53
Not the cause for failure, but you are not giving your springs "a break" by cycling them. Cycling is what wears springs, not leaving compressed/decompressed. That said, I'd be impressed if an a average guy could get a mag spring to fail from use.

gunplumber
May 11, 2015, 08:24
1 magazine does not establish a pattern.

And + 1 on cyclic spring fatigue. I have trouble getting people to understand that unloading the mags, and loading them again causes more wear than leaving them loaded. Not that either will have any practical effect.

mouthpiece
May 11, 2015, 11:07
It happens with the Polish mags, I have 1 that is cracked at the top simiarly, but not to that extent as the one shown, but it did crack at the floorplate and shit the spring, follower and bullets on the ground.

Only other mag I have cracked was a clear Bulgy Bullet mag, the rear lug broke off.

I stay with the steel European mags.

tdb59
May 11, 2015, 12:20
1 magazine does not establish a pattern.

.......

Yup.

Once a cat sits on a hot stove, it acts as though ALL stoves are hot.


.

Pluribus
May 11, 2015, 12:46
Didn't happen. AK's are way too incredible for that to ever happen. AK's are indestructible. AK's are the best engineered rifel in the wurld and never, ever break let alone malf. (malf is an operator phrase) If it was operated correctly, it wouldn't of malf'd. It's all a miss-use of a platform.

Plastic is for grocks cause it works on gunz, not clips.


:justkidding:

:wink:

gunplumber
May 11, 2015, 13:23
Is that a Polish mil-spec magazine, or the Polish version of TAPCO - like the Bulgarian TAPCO that makes the non-metal lined mag? I think I see metal lining in the feed lips of that one (the round spots are where the plastic and the liner interface?)

I've had parts from every kind of gun fail - including an uber-anal German Mp5 bolt carrier. Shit happens. It's possibly a fluke. But now someone else reports the same. From the same bad batch or a fundamental defect in manufacture? I'm just not sure it's time to ditch all the mags. I've been using DDR and Romy Bakelite 5.45 and Bulgy and Polish plastic for years and years with no issues. I think the blogger cited in the Babacus's post may be jumping to conclusions, to extrapolate a problem with one brand to be indicative synthetics in general.

I did have some 30 year old Chines bakelite crumble around the feed lips, but the metal liner held. I bought them (and they were expensive even back then) to color-coordinate my 56S-2.

http://www.arizonaresponsesystems.com/smith/ak/gallery-ak-china-02.jpg

Brian in MN
May 11, 2015, 14:16
They are crappy, commercial mags.


http://www.akfiles.com/forums/showthread.php?t=214144&highlight=polish+plastic+mags


I think all of you who extrapolate from this that all synthetic mags are junk should spread the gospel. It'll help keep the price down on milspec synthetics for the rest of us.

Pluribus
May 11, 2015, 15:08
They are crappy, commercial mags.


http://www.akfiles.com/forums/showthread.php?t=214144&highlight=polish+plastic+mags


I think all of you who extrapolate from this that all synthetic mags are junk should spread the gospel. It'll help keep the price down on milspec synthetics for the rest of us.

Sschwoooooo! I'm glad to hear that. So, the half dozen Radom circle 11 I may or, may not have should be good to go? I hope so, I don't think I can bare another internet rumour.

:thumbsup:

chet
May 11, 2015, 15:47
And + 1 on cyclic spring fatigue. I have trouble getting people to understand that unloading the mags, and loading them again causes more wear than leaving them loaded. Not that either will have any practical effect.

I've always wondered about the "rate of change" (for lack of a better term) in spring return rates.

It seems like some makes of mags start out extremely stiff and difficult to load and then "settle" into much lower return rate that really doesn't change again.
I guess the follower and mag body might smooth up a little in that initial break in but I really can't explain why new springs seem to plateau after just a few cycles instead of continuing to lose their rate of return.

gunplumber
May 11, 2015, 16:03
It is a subject that interests me. I'm particularly curious about rectangular springs, as my understanding was the larger radius created fewer stress risers in the spring formation.

Given the additional requirement of the spring is to stay at approximately the same location in the mag, I understand a rectangular shape facilitates this. HK likes them.

Maybe improvements in materials (chrome silicon?) allows for tighter bends?

Here's a page of notes that I compiled in some discussions with spring manufacturers - formulas didn't cut and paste.

Spring Fatigue

Q: Some say you should not keep magazines fully-loaded, but is this because of permanent spring deformation or just bad mechanical engineering design? ?

A: If the spring permanently deforms when you fully-load a mag, then I submit that such a spring is defective and should never have been sold. It will not fatigue. Fatigue is a function of cyclic loading.

Q: What about memory effect, strain hardening and plastic deformation ?

A: We are talking about regular steel alloys, not shape memory alloys There is no "memory effect A properly designed spring shouldn't plastically deform in the first place. So there is nothing to "remember." Anyway, with memory, we could just heat it and it would restore it self And creep just doesn't occur at room temperature. As a rule of thumb, creep processes occur at about 0.5Tm where Tm = melting temp. No, it fails for two reasons:

1) heating and cooling cycling loosens the wiring at its connections (typically outlets and junctions)
2) local heating due to the Al oxide layer producing high resistance (which exacerbates problem 1). It does not creep at room temperature

Creep mechanisms like grain boundary sliding, vacancy diffusion, thermal softening, and dislocation climb all require thermal activation

Q: So if the spring designer, and the metallurgist, are competent, there should be no fatigue in a spring that isn't stressed beyond its elastic modulus?

A: "Stressed beyond its elastic modulus" is technically incorrect. Elastic modulus E is the slope of the stress-strain curve. It provides an indication of the stiffness of the material. I assume that you mean to say "stressed beyond its static yield strength." However, fatigue can definitely occur due to cyclic loading below the static yield strength of the material. Even absent surface stress risers (e.g., notches), fatigue crack nucleation can occur at grain boundaries, second-phase particles, twin boundaries, and other microstructural features which exist normally.

Fatigue is a failure mode due to CYCLIC loading. A loaded magazine is a static situation, not a cyclically loaded one. Fatigue is not a bending type failure. It consists of crack nucleation/initiation, progressive cyclic crack growth, and catastrophic failure.

Fractographic examination of the material commonly shows "river markings", i.e. ridges or striations which delineate the cyclic crack propagation. Note, springs that must flex rapidly, like your recoil spring, can fatigue with use. The reason is that the rapid and repeated flexing can raise the spring temperature enough in localized stress risers

Q: I've never heard of this as a fatigue mechanism. My understanding is that fatigue failure is due to localized plastic deformation and dislocation (slip band) propagation and is not due to localized heating destroying the temper of the spring in that area. The load will then exceed the (reduced) elastic modulus at that point in the spring and fail.

A: As mentioned above, the use of the term "elastic modulus" here is incorrect. A load doesn't exceed the elastic modulus since E is the slope of the stress-strain curve and measures stiffness. What you probably mean to say is that "the load will then exceed the (reduced) yield strength...."
allow it to collapse or even break. But a static load within the spring's design limits, like that in a stored loaded magazine, should never have this problem. By definition, a static load (e.g., a once-loaded mag stored indefinitely) can never produce fatigue failure. You need a cyclic load (e.g., a repeatedly loaded and unloaded mag). If a spring is kept under constant compression it should not get worse over time.

For systems that obey Hooke's law, the extension produced is directly proportional to the load:

where:
is the distance that the spring has been stretched or compressed away from the equilibrium position, which is the position where the spring would naturally come to rest (usually in meters),
is the restoring force exerted by the material (usually in newtons), and
is the force constant (or spring constant). The constant has units of force per unit length (usually in newtons per meter).
When this holds, we say that the behavior is linear. If shown on a graph, the line should show a direct variation. There is a negative sign on the right hand side of the equation because the restoring force always acts in the opposite direction of the x displacement (when a spring is stretched to the left, it pulls back to the right).
Elastic materials
Objects that quickly regain their original shape after being deformed by a force, with the molecules or atoms of their material returning to the initial state of stable equilibrium, often obey Hooke's law.
We may view a rod of any elastic material as a linear spring. The rod has length L and cross-sectional area A. Its extension (strain) is linearly proportional to its tensile stress, σ by a constant factor, the inverse of its modulus of elasticity, E, hence,

or

Hooke's law only holds for some materials under certain loading conditions. Steel exhibits linear-elastic behavior in most engineering applications; Hooke's law is valid for it throughout its elastic range (i.e., for stresses below the yield strength). For some other materials, such as aluminium, Hooke's law is only valid for a portion of the elastic range. For these materials a proportional limit stress is defined, below which the errors associated with the linear approximation are negligible.
Rubber is generally regarded as a "non-hookean" material because its elasticity is stress dependent and sensitive to temperature and loading rate.
Applications of the law include spring operated weighing machines, stress analysis and modeling of materials.
[edit] The spring equation


Stress–strain curve for low-carbon steel. Hooke's law is only valid for the portion of the curve between the origin and the yield point.
1. Ultimate strength
2. Yield strength-corresponds to yield point.
3. Rupture
4. Strain hardening region
5. Necking region.
The most commonly encountered form of Hooke's law is probably the spring equation, which relates the force exerted by a spring to the distance it is stretched by a spring constant, k, measured in force per length.

The negative sign indicates that the force exerted by the spring is in direct opposition to the direction of displacement. It is called a "restoring force", as it tends to restore the system to equilibrium. The potential energy stored in a spring is given by

which comes from adding up the energy it takes to incrementally compress the spring. That is, the integral of force over distance. (Note that potential energy of a spring is always non-negative.)
This potential can be visualized as a parabola on the U-x plane. As the spring is stretched in the positive x-direction, the potential energy increases (the same thing happens as the spring is compressed). The corresponding point on the potential energy curve is higher than that corresponding to the equilibrium position (x = 0). The tendency for the spring is to therefore decrease its potential energy by returning to its equilibrium (unstretched) position, just as a ball rolls downhill to decrease its gravitational potential energy.
If a mass m is attached to the end of such a spring, the system becomes a harmonic oscillator. It will oscillate with a natural frequency given as either:
radians per second (angular frequency)
or
hertz (cycles per second)
where ν is frequency (the symbol is the Greek character nu and not the letter v) since .
The various lattice spring constants are to be included l

tdb59
May 11, 2015, 16:32
On the example of spring life, Mark, I purchased a recoil spring at the Great Western Show in Pomona about 1984 for my .38 Super Commander. It was made of square wire, labeled as 22#, and I never did replace it after thousands of rounds through the gun over 10 years. I have no idea who manufactured it, and never did find any more like it.

Thoughts ?

.

chet
May 11, 2015, 16:34
So, would that mean that possibly some part of the spring is not reacting in a linear manner and instead "fails" during the break in period and then, what's left, is the sections or aspects of the spring that works?

gunplumber
May 11, 2015, 16:46
I'm a smart guy (just ask me), but this is an area I'm still learning. I think I understand some parts of it, but don't take my pondering as authoritative.

I can picture microscopic cracks at the bends. I imagine that the sharper the radius of the bend, the more likely the cracks will be present. Now we apply cycling. If I bend a paperclip back and forth just a few times to break it, I can immediately feel the heat generated. So it stands to reason that a rapid compression and expansion of a spring will generate heat, and the heat will have greatest affect at the bends - and the sharper the bend, the greater the affect. But it would have to reach a high temperature - maybe 300F+ before resulting in the heat annealing the metal and killing its "springiness". Maybe it's possible for high temperatures to be localized at such a small area that the not discernible to a user, but will expand the microscopic fissures?

No idea on square wire.

Another are we discussed, although I can't find my notes on it, is the concept of a spring going solid. That is, the spring is completely stacked on top of itself with no space between the coils. This is supposed to be bad, but I don't understand why. The length of the AR-15 mag, combined with its capacity, can result in the spring "going solid" with 20 rds. The AK mag follower has longer flanges on the sides than the length of the mag spring at its full solid state, thus it can never go solid. Was this just by chance or a design feature?

tdb59
May 11, 2015, 18:03
Another are we discussed, although I can't find my notes on it, is the concept of a spring going solid. That is, the spring is completely stacked on top of itself with no space between the coils. This is supposed to be bad, but I don't understand why.

Isn't coil bind the point at which spring rate is determined ?


ETA: Valve springs in an engine can fail in a shortened time frame if they bind at static load. Of course at operational speed there is a mass load that causes a " hammering " effect of sorts.


.

chet
May 11, 2015, 18:24
One of the manufacturers had a rep on a TV show the other day and he was watching a design team develop a pistol magazine. He said it was easier to develop the mag first and then build the gun around it than it was to design a handgun and then design the mag to fit it and function in it afterwards.


Springs. How do they work?

Brian in MN
May 11, 2015, 21:13
IMHO the thing that wears out good quality black rifle mags has nothing to do with the spring. It has everything to do with almost no one knowing how to unload a mag properly resulting in worn out feed lips. This is also why the Russians fielded metal mags with feed lips that look like they were designed by an engineer from the Caterpillar Corp. I probably own close to 200 military surplus mags of various flavors. I have never bought one and discovered a worn out spring.

That and silly tactical mag changes that result in beating the crap out of them as they hit the deck. The latter is why I never buy from Mall Ninja Surplus.

Having said that, I generally leave the mags I use loaded unless I actually have a reason to unload them like getting caught in the rain or bringing them indoors after being out in cold weather.

hueyville
May 12, 2015, 00:20
Why does someone leave loaded magazines in safe? My vaults are all fire rated but in raging fully involved house fire inside of safe could get hot enough for rounds cook off starting fire inside safe as most full of carpet. Rim fire will start cooking off at 275 F and center fire will pop between 300 and 400 F. The case becomes the projectile but doesn't have killing velocity but a bunch could really ding up your guns or burn them from inside out if enough oxygen in safe. All my ammo is stored in OSHA explosion proof fire lockers. A 50 caliber ammo can can build enough pressure to pop the lid off.

I keep two magazine pouches with loaded magazines hanging on hook next to vaults. If have to open quickly and put into action the AR15 safe has a loaded eight mag pouch next to it and battle rifle safe has a six mag pouch hanging next to it. Yes if house burns I lose 14 mags. Majority of metal magazines are in safes unloaded. Plastic and poly are likely going to melt so don't waste room in safe for them.

Interesting read:
http://my.firefighternation.com/m/discussion?id=889755%3ATopic%3A4568957

Right Side Up
May 12, 2015, 00:27
Isn't coil bind the point at which spring rate is determined ?


ETA: Valve springs in an engine can fail in a shortened time frame if they bind at static load. Of course at operational speed there is a mass load that causes a " hammering " effect of sorts.


.

True. In a racing engine setting a spring too far from coil bind can make it fail too. When the valvetrain goes into *loft*, the distance from coil bind sets the limit for how far the valve lofts. Lots of times we'll shim a valve spring on a high rpm engine spring closer to coil bind (like .040"-.070"). The springs last longer, and the engine spins more rpm before valve float. Weird, I know.

gunplumber
May 12, 2015, 07:49
Why does someone leave loaded magazines in safe?

Cause some amateurs only have a few mags, so they hide them in the safe in shame. Mine take up 12 -15 bins on 3 shelves, and I've downsized to just AR, AK74, Glock 17 and SCAR mags. 200 just don't fit in a safe very well. And yes, I keep them loaded. Range time is precious to me, so I can load mags in front of the TV.

def90
May 19, 2015, 09:00
Those mags are the crappy commercial mags without the metal inserts in them.. They keep getting sold as Bulgarian surplus but they are not..

mouthpiece
May 19, 2015, 09:50
Those mags are the crappy commercial mags without the metal inserts in them.. They keep getting sold as Bulgarian surplus but they are not..

Which those mags are you referring to?
The Polish mags have steel front and rear lugs, I don't recall on the feedlip area.

def90
May 19, 2015, 11:28
Which those mags are you referring to?
The Polish mags have steel front and rear lugs, I don't recall on the feedlip area.

I know the cheap commercial ones are the only ones that have the caliber stamps on them as the mag shown above. The Bulgarian ones do not have the metal inserts, not sure of the Polish. Both have the same reputation as far as quality goes.

catmguy445
May 21, 2015, 11:09
One of the manufacturers had a rep on a TV show the other day and he was watching a design team develop a pistol magazine. He said it was easier to develop the mag first and then build the gun around it than it was to design a handgun and then design the mag to fit it and function in it afterwards.

Messr's Dornaus & Dixon found that out the hard way.

akass
May 21, 2015, 20:22
Remember the first poly black Polish 762x39 mags AIM sold around 2002 that developed cracks near the top of the mags?
I had the floor plate lips break off by themselves on one of these unloaded mags.
I opened the safe one day,and found the spring sticking out of the bottom of the mag.Super glued it,and still holding together to this day.